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Sonntag, 13. August 2017 - 22:45 Uhr

Astronomie - TRAPPIST-1 ist älter als unser Sonnensystem

13.08.2017

 
This illustration shows what the TRAPPIST-1 system.
 
 
TRAPPIST-1 is an ultra-cool dwarf star in the constellation Aquarius.
TRAPPIST-1 is an ultra-cool dwarf star in the constellation Aquarius, and its seven planets orbit very close to it. Image Credit: NASA/JPL-Caltech
› Full image and caption

If we want to know more about whether life could survive on a planet outside our solar system, it's important to know the age of its star. Young stars have frequent releases of high-energy radiation called flares that can zap their planets' surfaces. If the planets are newly formed, their orbits may also be unstable. On the other hand, planets orbiting older stars have survived the spate of youthful flares, but have also been exposed to the ravages of stellar radiation for a longer period of time.

Scientists now have a good estimate for the age of one of the most intriguing planetary systems discovered to date -- TRAPPIST-1, a system of seven Earth-size worlds orbiting an ultra-cool dwarf star about 40 light-years away. Researchers say in a new study that the TRAPPIST-1 star is quite old: between 5.4 and 9.8 billion years. This is up to twice as old as our own solar system, which formed some 4.5 billion years ago.

The seven wonders of TRAPPIST-1 were revealed earlier this year in a NASA news conference, using a combination of results from the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, NASA's Spitzer Space Telescope, and other ground-based telescopes. Three of the TRAPPIST-1 planets reside in the star's "habitable zone," the orbital distance where a rocky planet with an atmosphere could have liquid water on its surface. All seven planets are likely tidally locked to their star, each with a perpetual dayside and nightside.

At the time of its discovery, scientists believed the TRAPPIST-1 system had to be at least 500 million years old, since it takes stars of TRAPPIST-1's low mass (roughly 8 percent that of the Sun) roughly that long to contract to its minimum size, just a bit larger than the planet Jupiter. However, even this lower age limit was uncertain; in theory, the star could be almost as old as the universe itself. Are the orbits of this compact system of planets stable? Might life have enough time to evolve on any of these worlds?

"Our results really help constrain the evolution of the TRAPPIST-1 system, because the system has to have persisted for billions of years. This means the planets had to evolve together, otherwise the system would have fallen apart long ago," said Adam Burgasser, an astronomer at the University of California, San Diego, and the paper's first author. Burgasser teamed up with Eric Mamajek, deputy program scientist for NASA's Exoplanet Exploration Program based at NASA's Jet Propulsion Laboratory, Pasadena, California, to calculate TRAPPIST-1's age. Their results will be published in The Astrophysical Journal.

It is unclear what this older age means for the planets' habitability. On the one hand, older stars flare less than younger stars, and Burgasser and Mamajek confirmed that TRAPPIST-1 is relatively quiet compared to other ultra-cool dwarf stars. On the other hand, since the planets are so close to the star, they have soaked up billions of years of high-energy radiation, which could have boiled off atmospheres and large amounts of water. In fact, the equivalent of an Earth ocean may have evaporated from each TRAPPIST-1 planet except for the two most distant from the host star: planets g and h. In our own solar system, Mars is an example of a planet that likely had liquid water on its surface in the past, but lost most of its water and atmosphere to the Sun's high-energy radiation over billions of years.

However, old age does not necessarily mean that a planet's atmosphere has been eroded. Given that the TRAPPIST-1 planets have lower densities than Earth, it is possible that large reservoirs of volatile molecules such as water could produce thick atmospheres that would shield the planetary surfaces from harmful radiation. A thick atmosphere could also help redistribute heat to the dark sides of these tidally locked planets, increasing habitable real estate. But this could also backfire in a "runaway greenhouse" process, in which the atmosphere becomes so thick the planet surface overheats - as on Venus.

"If there is life on these planets, I would speculate that it has to be hardy life, because it has to be able to survive some potentially dire scenarios for billions of years," Burgasser said.

Fortunately, low-mass stars like TRAPPIST-1 have temperatures and brightnesses that remain relatively constant over trillions of years, punctuated by occasional magnetic flaring events. The lifetimes of tiny stars like TRAPPIST-1 are predicted to be much, much longer than the 13.7 billion-year age of the universe (the Sun, by comparison, has an expected lifetime of about 10 billion years).

"Stars much more massive than the Sun consume their fuel quickly, brightening over millions of years and exploding as supernovae," Mamajek said. "But TRAPPIST-1 is like a slow-burning candle that will shine for about 900 times longer than the current age of the universe."

Some of the clues Burgasser and Mamajek used to measure the age of TRAPPIST-1 included how fast the star is moving in its orbit around the Milky Way (speedier stars tend to be older), its atmosphere's chemical composition, and how many flares TRAPPIST-1 had during observational periods. These variables all pointed to a star that is substantially older than our Sun.

Future observations with NASA's Hubble Space Telescope and upcoming James Webb Space Telescope may reveal whether these planets have atmospheres, and whether such atmospheres are like Earth's.

"These new results provide useful context for future observations of the TRAPPIST-1 planets, which could give us great insight into how planetary atmospheres form and evolve, and persist or not," said Tiffany Kataria, exoplanet scientist at JPL, who was not involved in the study.

Future observations with Spitzer could help scientists sharpen their estimates of the TRAPPIST-1 planets' densities, which would inform their understanding of their compositions.

Quelle: NASA

 
 
 
 

Tags: Astronomie - TRAPPIST-1 ist älter als unser Sonnensystem 

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Sonntag, 13. August 2017 - 22:30 Uhr

Raumfahrt - Cassini Grand Finale Around Saturn -Update-3

24.06.2017

Witness Cassini's Finale at Saturn Live from JPL

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Cassini Project Manager Earl Maize waits for the spacecraft's signal at the start of the "Grand Finale" mission phase with the operations team in mission control at JPL on April 26, 2017. Credit: NASA/JPL-Caltech

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Social media users may apply for access to a two-day event culminating in the triumphant end of NASA's Cassini mission to Saturn after nearly 20 years in space. Up to 25 selected participants for the September 14-15, 2017, event will tour, explore and share their experiences from NASA's Jet Propulsion Laboratory in Pasadena, California. 

Writers, vloggers, photographers, educators, students, artists and other curious minds who use social media to engage specific audiences are encouraged to apply.

Selected attendees will tour JPL, including a visit to mission control and the Spacecraft Assembly Facility; meet Cassini mission scientists and engineers; and share in the final moments of the Cassini mission, live from the JPL media site, as the spacecraft makes a fateful plunge into Saturn's atmosphere on Sept. 15, ending its long and discovery-rich mission.

NASA Social applications may be submitted through June 29, 2017. To apply, visit:

https://go.nasa.gov/cassini-social

During its journey, Cassini has made many discoveries, including a global ocean with hydrothermal activity within Saturn's moon Enceladus, and vast seas of liquid methane on the planet's largest moon, Titan. Cassini began the final, dramatic phase of its mission, called the Grand Finale, on April 26, with the first of planned 22 dives between Saturn and its rings. The finale orbits bring the spacecraft closer to Saturn than ever before, providing stunning, high-resolution images and new insights into the planet's interior structure and the origins of the rings. During its final plunge into Saturn, Cassini will send data about the atmosphere's composition until its signal is lost.

More information about Cassini's Grand Finale, including multimedia, is available at:

https://saturn.jpl.nasa.gov/grandfinale

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. JPL designed, developed and assembled the Cassini orbiter.

More information about Cassini is at:

https://www.nasa.gov/cassini

https://saturn.jpl.nasa.gov

Get more information about NASA social media at:

http://www.nasa.gov/socialmedia

Interact with the Cassini mission on social media via:

https://twitter.com/CassiniSaturn

https://www.facebook.com/NASACassini/

 

Quelle: NASA

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Update: 29.06.2017

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Small Wonders

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This montage of views from NASA's Cassini spacecraft shows three of Saturn's small ring moons: Atlas, Daphnis and Pan at the same scale for ease of comparison.

 

Two differences between Atlas and Pan are obvious in this montage. Pan's equatorial band is much thinner and more sharply defined, and the central mass of Atlas (the part underneath the smooth equatorial band) appears to be smaller than that of Pan.

 

Images of Atlas and Pan taken using infrared, green and ultraviolet spectral filters were combined to create enhanced-color views, which highlight subtle color differences across the moons' surfaces at wavelengths not visible to human eyes. (The Daphnis image was colored using the same green filter image for all three color channels, adjusted to have a realistic appearance next to the other two moons.)

 

A version of the montage using only monochrome images is also provided here.

 

 

All of these images were taken using the Cassini spacecraft narrow-angle camera. The images of Atlas were acquired on April 12, 2017, at a distance of 10,000 miles (16,000 kilometers) and at a sun-moon-spacecraft angle (or phase angle) of 37 degrees. The images of Pan were taken on March 7, 2017, at a distance of 16,000 miles (26,000 kilometers) and a phase angle of 21 degrees. The Daphnis image was obtained on Jan. 16, 2017, at a distance of 17,000 miles (28,000 kilometers) and at a phase angle of 71 degrees. All images are oriented so that north is up.

Quelle: NASA

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Update: 11.07.2017

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Dawn’s Early Light

pia21336-full

The light of a new day on Saturn illuminates the planet’s wavy cloud patterns and the smooth arcs of the vast rings.

 

The light has traveled around 80 minutes since it left the sun's surface by the time it reaches Saturn. The illumination it provides is feeble; Earth gets 100 times the intensity since it's roughly ten times closer to the sun. Yet compared to the deep blackness of space, everything at Saturn still shines bright in the sunlight, be it direct or reflected.

 

This view looks toward the sunlit side of the rings from about 10 degrees above the ring plane. The image was taken with the Cassini spacecraft wide-angle camera on Feb. 25, 2017 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 939 nanometers.

 

The view was obtained at a distance of approximately 762,000 miles (1.23 million kilometers) from Saturn. Image scale is 45 miles (73 kilometers) per pixel.

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Saturnian Dawn

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NASA's Cassini spacecraft peers toward a sliver of Saturn's sunlit atmosphere while the icy rings stretch across the foreground as a dark band.

 

This view looks toward the unilluminated side of the rings from about 7 degrees below the ring plane. The image was taken in green light with the Cassini spacecraft wide-angle camera on March 31, 2017.

 

The view was obtained at a distance of approximately 620,000 miles (1 million kilometers) from Saturn. Image scale is 38 miles (61 kilometers) per pixel.

Quelle: NASA

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Update: 20.07.2017

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Liftoff? Icy Jets of Saturn Moon Enceladus Fly in NASA Photo

 
Saturn's moon Enceladus releases jets of water ice as imaged by the Cassini spacecraft in April. The moon shines in reflected Saturn light, while the jets are backlit by the sun.
Credit: NASA/JPL-Caltech/Space Science Institute

A photo of Saturn's moon Enceladus looks poised for liftoff as jets fly from its southern hemisphere.

While Enceladus can't fly — at least outside of its ordinary orbit around the ringed planet — its remarkable icy jets intrigue scientists because they hint at a subsurface ocean that could support life.

The photo, taken by the Cassini spacecraft, spotlights the moon's Saturn-facing hemisphere, which is 313 miles across (504 km), according to NASA's image caption. The jets are backlit by sunlight, while the front shines with light reflected back from Saturn. Cassini was 502,000 miles (808,000 km) from Enceladus when it captured the visible-light image with its narrow-angle camera on April 13, and the image shows 3 miles (5 km) per pixel.

 

 

 

Enceladus' fierce jets emerge from a series of ridges in its southern hemisphere nicknamed "tiger stripes." Cassini first spotted the jets in 2005, and dove through the plumes multiple times; in 2015, it passed within 30 miles(50 km) of the moon's surface while sampling their composition. Data from that flyby suggested that its subsurface ocean might have enough energy, suggested by the existence of molecular hydrogen, to host life similar to microbes on Earth. Besides water ice, the plumes contain traces of methane, ammonia, carbon monoxide, carbon dioxide, salts and simple organic molecules. 

Cassini is a collaboration among NASA, the European Space Agency and the Italian Space Agency, and it has orbited Saturn since 2004. The probe is in the Grand Finale phase of its mission, as it makes close flybys between Saturn and its rings before plunging down into the planet's atmosphere Sept. 15. That dive is partially motivated by a desire to protect the little icy moon — as Cassini ran out of fuel, its orbit could have become unstable and led to it crashing and contaminating moons in Saturn's neighborhood. 

Quelle: SC

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Update: 25.07.2017

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Saturn Surprises As Cassini Continues its Grand Finale

Mosaic combines views captured by Cassini
This mosaic combines views captured by Cassini as it made the first dive of the mission's Grand Finale on April 26, 2017, and shows details in bands and swirls in the atmosphere.
Credits: NASA/JPL-Caltech/SSI/Hampton University
Recent images of features in Saturn's C ring
Recent images of features in Saturn's C ring called "plateaus" reveal a streaky texture that is very different from the textures of the regions around them.
Credits: NASA/JPL-Caltech/Space Science Institute
Recent images of features in Saturn's C ring
Recent images of features in Saturn's C ring called "plateaus" reveal a streaky texture that is very different from the textures of the regions around them.
Credits: NASA/JPL-Caltech/Space Science Institute
Recent images of features in Saturn's C ring
Recent images of features in Saturn's C ring called "plateaus" reveal a streaky texture that is very different from the textures of the regions around them.
Credits: NASA/JPL-Caltech/Space Science Institute
Data collected by Cassini's Radio and Plasma Wave Science instrument
This colorful spectrogram represents data collected by Cassini's Radio and Plasma Wave Science instrument as it crossed through Saturn's D ring on May 28, 2017.
Credits: NASA/JPL-Caltech/University of Iowa
False-color view from NASA's Cassini spacecraft
This false-color view from NASA's Cassini spacecraft gazes toward the rings beyond Saturn's sunlit horizon, where a thin haze can be seen along the limb.
Credits: NASA/JPL-Caltech/Space Science Institute
Cassini captured the near-infrared images in this mosaic on June 29, 2017
Cassini captured the near-infrared images in this mosaic on June 29, 2017, as it raced toward the gap between Saturn and its rings.
Credits: NASA/JPL-Caltech/SSI/Hampton University

As NASA's Cassini spacecraft makes its unprecedented series of weekly dives between Saturn and its rings, scientists are finding -- so far -- that the planet's magnetic field has no discernible tilt. This surprising observation, which means the true length of Saturn's day is still unknown, is just one of several early insights from the final phase of Cassini's mission, known as the Grand Finale.

 

Other recent science highlights include promising hints about the structure and composition of the icy rings, along with high-resolution images of the rings and Saturn's atmosphere.

 

Cassini is now in the 15th of 22 weekly orbits that pass through the narrow gap between Saturn and its rings. The spacecraft began its finale on April 26 and will continue its dives until Sept. 15, when it will make a mission-ending plunge into Saturn's atmosphere.

 

"Cassini is performing beautifully in the final leg of its long journey," said Cassini Project Manager Earl Maize at NASA's Jet Propulsion Laboratory, Pasadena, California. "Its observations continue to surprise and delight as we squeeze out every last bit of science that we can get."

 

Cassini scientists are thrilled as well -- and surprised in some cases -- with the observations being made by the spacecraft in the finale. "The data we are seeing from Cassini's Grand Finale are every bit as exciting as we hoped, although we are still deep in the process of working out what they are telling us about Saturn and its rings," said Cassini Project Scientist Linda Spilker at JPL.

 

Early Magnetic Field Analysis

 

Based on data collected by Cassini's magnetometer instrument, Saturn's magnetic field appears to be surprisingly well-aligned with the planet's rotation axis. The tilt is much smaller than 0.06 degrees -- which is the lower limit the spacecraft's magnetometer data placed on the value prior to the start of the Grand Finale.

 

This observation is at odds with scientists' theoretical understanding of how magnetic fields are generated. Planetary magnetic fields are understood to require some degree of tilt to sustain currents flowing through the liquid metal deep inside the planets (in Saturn's case, thought to be liquid metallic hydrogen). With no tilt, the currents would eventually subside and the field would disappear.

 

Any tilt to the magnetic field would make the daily wobble of the planet's deep interior observable, thus revealing the true length of Saturn's day, which has so far proven elusive.

 

"The tilt seems to be much smaller than we had previously estimated and quite challenging to explain," said Michele Dougherty, Cassini magnetometer investigation lead at Imperial College, London. "We have not been able to resolve the length of day at Saturn so far, but we're still working on it."

 

The lack of a tilt may eventually be rectified with further data. Dougherty and her team believe some aspect of the planet's deep atmosphere might be masking the true internal magnetic field. The team will continue to collect and analyze data for the remainder of the mission, including during the final plunge into Saturn.

 

The magnetometer data will also be evaluated in concert with Cassini's measurements of Saturn's gravity field collected during the Grand Finale. Early analysis of the gravity data collected so far shows discrepancies compared with parts of the leading models of Saturn's interior, suggesting something unexpected about the planet's structure is awaiting discovery.

 

Sampling Saturn

 

In addition to its investigation of the planet's interior, Cassini has now obtained the first-ever samples of the planet's atmosphere and main rings, which promise new insights about their composition and structure. The spacecraft's cosmic dust analyzer (CDA) instrument has collected many nanometer-size ring particles while flying through the planet-ring gap, while its ion and neutral mass spectrometer (INMS) has sniffed the outermost atmosphere, called the exosphere.

 

During Cassini's first dive through the gap on April 26, the spacecraft was oriented so its large, saucer-shaped antenna would act as a shield against oncoming ring particles that might cause damage. While at first it appeared that there were essentially no particles in the gap, scientists later determined the particles there are very small and could be detected using the CDA instrument.

 

The cosmic dust analyzer was later allowed to peek out from behind the antenna during Cassini's third of four passes through the innermost of Saturn's main rings, the D ring, on June 29. During Cassini's first two passes through the inner D ring, the particle environment there was found to be benign. This prompted mission controllers to relax the shielding requirement for one orbit, in hopes of capturing ring particles there using CDA. As the spacecraft passed through the ring, the CDA instrument successfully captured some of the tiniest particles there, which the team expects will provide significant information about their composition.

 

During the spacecraft's final five orbits, as well as it final plunge, the INMS instrument will obtain samples deeper down in the atmosphere. Cassini will skim through the outer atmosphere during these passes, and INMS is expected to send particularly important data on the composition of Saturn's atmosphere during the final plunge.

 

Amazing Images

 

Not to be outdone, Cassini's imaging cameras have been hard at work, returning some of the highest-resolution views of the rings and planet they have ever obtained. For example, close-up views of Saturn's C ring -- which features mysterious bright bands called plateaus -- reveal surprisingly different textures in neighboring sections of the ring. The plateaus appear to have a streaky texture, whereas adjacent regions appear clumpy or have no obvious structure at all. Ring scientists believe the new level of detail may shed light on why the plateaus are there, and what is different about the particles in them.

 

On two of Cassini's close passes over Saturn, on April 26 and June 29, the cameras captured ultra-close views of the cloudscape racing past, showing the planet from closer than ever before. Imaging scientists have combined images from these dives into two new image mosaics and a movie sequence. (Specifically, the previously released April 26 movie was updated to greatly enhance its contrast and sharpness.)

 

Launched in 1997, Cassini has orbited Saturn since arriving in 2004 for an up-close study of the planet, its rings and moons, and its vast magnetosphere. Cassini has made numerous dramatic discoveries, including a global ocean with indications of hydrothermal activity within the moon Enceladus, and liquid methane seas on another moon, Titan.

 

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the mission for NASA's Science Mission Directorate, Washington. JPL designed, developed and assembled the Cassini orbiter.

Quelle: NASA

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Update: 1.08.2017

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Saturn Surprises Right Up Until Cassini’s End

Saturn keeps its secrets as NASA's Cassini spacecraft heads towards its September grand finale.

Saturn Cassini

An alien vista stretches out before Cassini, in this false color image taken by the spacecraft's narrow angle camera on July 16th. You can just see the thin haze of the planet's upper atmosphere on the lit limb, with the rings beyond. 
NASA/JPL-Caltech/Space Science Institute

The ringed planet seems to be hanging on to at least some of its secrets right up until the very end.

NASA's Cassini spacecraft is now in the midst of a series of dramatic weekly Grand Finale dives through the gap between Saturn and its ring system. This follows a series of wider Ring Grazing Orbits spanning late 2016 into earlier this year, and will climax with the end of the mission itself in September.

Cassini is performing beautifully in the final leg of its long journey," says Earl Maize (NASA-JPL) in a recent press release. "Its observations continue to surprise and delight as we squeeze out every last bit of science that we can get."

Cassini is now in the 16th of a total of 22 weekly orbits, coming as close as 1,900 miles to the planet's cloud tops. This allows the mission to not only examine the magnetic field of the planet close up, but also allows Cassini a chance to sample the upper atmosphere of the planet itself.

These final orbits are a bit of a risk, as the spacecraft must thread its way through the ring plane at 77,000 mph. This elevated risk is one reason that researchers have held off on the exploration of Saturn close-up until now.

Saturn Noodle

A "noodle mosaic" of Saturn, composed of 137 images from the first Grand Finale dive in April, shows the pole (upper left) down to the planet's equator (bottom right). 
NASA / JPL-Caltech / Space Science Institute

Science at Saturn

One of the strangest recent findings from Cassini is what it didn't find: much of a discernible difference in tilt between Saturn's rotational axis and its magnetic field. In other planets, this tilt sustains the dynamos that emanate from liquid metal cores. Think of Earth, where liquid iron in its outer core generates our protective magnetic field — and a magnetic pole offset from Earth's true, rotational pole.

Cassini's magnetometer has found that Saturn's magnetic pole — in this case, generated by liquid metallic hydrogen in its core — is remarkably well aligned with the planet's rotational axis, down to less than 0.06 degrees. This finding flies in the face of how we think planetary magnetic fields are generated, suggesting that we don't understand Saturn's internal structure as well as we thought we did.

The surprisingly good alignment also masks the true length of Saturn's day. While we see the planet's cloud tops spinning once every 10 hours, 14 minutes near the planet's equator, a gaseous planet doesn't all rotate at the same rate so its rotation changes at the poles. A discernible tilt in the magnetic field would make the planet wobble, betraying its true rotational speed. Since scientists haven't been able to measure the wobble, the length of Saturn's day remains a mystery.

Plus, check out these amazing new views of aurora over the limb of Saturn, shot by Cassini on July 20, 2017:

Taking Samples of Saturn

On the first plunge through the ring plane, Cassini went “dish first,” using its large radio antenna to protect the bulk of the spacecraft while a few instruments made tentative peeks out around the edges to "sniff" the local environment. But as researchers discovered the gap between the planet and the rings is — at least where Cassini sampled it — surprisingly devoid of debris, engineers relaxed constraints somewhat on subsequent passages, bringing other instruments to bear. Cassini has since used its Ion and Neutral Mass Spectrometer (INMS) to sample the tenuous exosphere of Saturn's atmosphere and its Cosmic Dust Analyzer (CDA) to sample the few ring particles obtained on each pass.

Saturn C-ring

The strange "streaky texture" of Saturn's C-ring. 
NASA / JPL-Caltech / Space Science Institute.

What's next? Cassini will dive deeper still on final passes and the INMS is expected to get better atmospheric samples on each pass. And of course, we've getting some thrilling up close images of Saturn itself, with more to come.

Launched two decades ago in 1997, the Cassini mission promises a thrill ride to the very last moment, just over one month away. Cassini is on a ballistic date with destiny, meaning that even if the spacecraft were to fall silent, destruction via atmospheric entry on September 15th is assured. But the science results will continue to pay off for years to come.

Not bad for a spacecraft launched last century.

Quelle: Sky&Telescope

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Update: 10.08.2017

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Cassini to Begin Final Five Orbits Around Saturn

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This artist's rendering shows Cassini as the spacecraft makes one of its final five dives through Saturn's upper atmosphere in August and September 2017.
Credits: NASA/JPL-Caltech

NASA's Cassini spacecraft will enter new territory in its final mission phase, the Grand Finale, as it prepares to embark on a set of ultra-close passes through Saturn’s upper atmosphere with its final five orbits around the planet.

 

Cassini will make the first of these five passes over Saturn at 12:22 a.m. EDT Monday, Aug. 14. The spacecraft's point of closest approach to Saturn during these passes will be between about 1,010 and 1,060 miles (1,630 and 1,710 kilometers) above Saturn's cloud tops.

 

The spacecraft is expected to encounter atmosphere dense enough to require the use of its small rocket thrusters to maintain stability – conditions similar to those encountered during many of Cassini's close flybys of Saturn's moon Titan, which has its own dense atmosphere.

 

"Cassini's Titan flybys prepared us for these rapid passes through Saturn's upper atmosphere," said Earl Maize, Cassini project manager at NASA's Jet Propulsion Laboratory (JPL) in California. "Thanks to our past experience, the team is confident that we understand how the spacecraft will behave at the atmospheric densities our models predict."

 

Maize said the team will consider the Aug. 14 pass nominal if the thrusters operate between 10 and 60 percent of their capability. If the thrusters are forced to work harder – meaning the atmosphere is denser than models predict – engineers will increase the altitude of subsequent orbits. Referred to as a "pop-up maneuver,” thrusters will be used to raise the altitude of closest approach on the next passes, likely by about 120 miles (200 kilometers).

 

If the pop-up maneuver is not needed, and the atmosphere is less dense than expected during the first three passes, engineers may alternately use the "pop-down" option to lower the closest approach altitude of the last two orbits, also likely by about 120 miles (200 kilometers). Doing so would enable Cassini's science instruments, especially the ion and neutral mass spectrometer (INMS), to obtain data on the atmosphere even closer to the planet's cloud tops.

 

"As it makes these five dips into Saturn, followed by its final plunge, Cassini will become the first Saturn atmospheric probe," said Linda Spilker, Cassini project scientist at JPL. "It's long been a goal in planetary exploration to send a dedicated probe into the atmosphere of Saturn, and we're laying the groundwork for future exploration with this first foray."

 

Other Cassini instruments will make detailed, high-resolution observations of Saturn's auroras, temperature, and the vortexes at the planet's poles. Its radar will peer deep into the atmosphere to reveal small-scale features as fine as 16 miles (25 kilometers) wide – nearly 100 times smaller than the spacecraft could observe prior to the Grand Finale.

 

On Sept. 11, a distant encounter with Titan will serve as a gravitational version of a large pop-down maneuver, slowing Cassini’s orbit around Saturn and bending its path slightly to send the spacecraft toward its Sept. 15 plunge into the planet.

 

During the half-orbit plunge, the plan is to have seven Cassini science instruments, including INMS, turned on and reporting measurements in near real time. The spacecraft is expected to reach an altitude where atmospheric density is about twice what it encountered during its final five passes. Once Cassini reaches that point, its thrusters will no longer be able to work against the push of Saturn’s atmosphere to keep the spacecraft's antenna pointed toward Earth, and contact will permanently be lost. The spacecraft will break up like a meteor moments later, ending its long and rewarding journey.

 

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. JPL manages the mission for NASA's Science Mission Directorate in Washington. JPL designed, developed and assembled the Cassini spacecraft.

Quelle: NASA

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Update: 13.08.2017

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Cassini's Final Titan Radar Swath
 
 
Two Titans
 
 
Highlighting Titan's Hazes
 
 
 
 
These two views of Saturn's moon Titan exemplify how NASA's Cassini spacecraft has revealed the surface of this fascinating world. Image Credit: NASA/JPL-Caltech/Space Science Institute
› Full image and caption

Mere weeks away from its dramatic, mission-ending plunge into Saturn, NASA's Cassini spacecraft has a hectic schedule, orbiting the planet every week in its Grand Finale. On a few orbits, Saturn's largest moon, Titan, has been near enough to tweak Cassini's orbit, causing the spacecraft to approach Saturn a bit closer or a bit farther away. A couple of those distant passes even pushed Cassini into the inner fringes of Saturn's rings.

 

Titan will be waiting once again when the road runs out in September. A last, distant encounter with the moon on Sept. 11 will usher Cassini to its fate, with the spacecraft sending back precious science data until it loses contact with Earth.

 

But this gravitational pushing and shoving isn't a new behavior for Titan. It's been doing that all along, by design.

 

Repeated flybys of Titan were envisioned, from the mission's beginning, as a way to explore the mysterious planet-size moon and to fling Cassini toward its adventures in the Saturn system. Scientists had been eager for a return to Titan since NASA's Voyager 1 spacecraft flew past in 1980 and was unable to see through the dense, golden haze that shrouds its surface.

 

Titan is just a bit larger than the planet Mercury. Given its size, the moon has significant gravity, which is used for bending Cassini's course as it orbits Saturn. A single close flyby of Titan could provide more of a change in velocity than the entire 90-minute engine burn the spacecraft needed to slow down and be captured by Saturn's gravity upon its arrival in 2004.

 

The mission's tour designers -- engineers tasked with plotting the spacecraft's course, years in advance -- used Titan as their linchpin. Frequent passes by the moon provided the equivalent of huge amounts of rocket propellant. Using Titan, Cassini's orbit could be stretched out, farther from Saturn -- for example, to send the spacecraft toward the distant moon Iapetus. With this technique, engineers used Titan flybys to change the orientation of Cassini's orbit many times during the mission; for example, lifting the spacecraft out of the plane of the rings to view them from high above, along with high northern and southern latitudes on Saturn and its moons.

 

What We've Learned

 

Over the course of its 13-year mission at Saturn, Cassini has made 127 close flybys of Titan, with many more-distant observations. Cassini also dropped off the European Space Agency's Huygens probe, which descended through Titan's atmosphere to land on the surface in January 2005.

 

Successes for Cassini during its mission include the revelation that, as researchers had theorized, there were indeed bodies of open liquid hydrocarbons on Titan's surface. Surprisingly, it turned out Titan's lakes and seas are confined to the poles, with almost all of the liquid being at northern latitudes in the present epoch. Cassini found that most of Titan has no lakes, with vast stretches of linear dunes closer to the equator similar to those in places like Namibia on Earth. The spacecraft observed giant hydrocarbon clouds hovering over Titan's poles and bright, feathery ones that drifted across the landscape, dropping methane rain that darkened the surface. There were also indications of an ocean of water beneath the moon's icy surface.

 

Early on, Cassini's picture of Titan was spotty, but every encounter built upon the previous one. Over the course of the entire mission, Cassini's radar investigation imaged approximately 67 percent of Titan's surface, using the spacecraft's large, saucer-shaped antenna to bounce signals off the moon's surface. Views from Cassini's imaging cameras, infrared spectrometer, and radar slowly and methodically added details, building up a more complete, high-resolution picture of Titan.

 

"Now that we've completed Cassini's investigation of Titan, we have enough detail to really see what Titan is like as a world, globally," said Steve Wall, deputy lead of Cassini's radar team at NASA's Jet Propulsion Laboratory in Pasadena, California.

 

Scientists now have enough data to understand the distribution of Titan's surface features (like mountains, dunes and seas) and the behavior of its atmosphere over time, and they have been able to begin piecing together how surface liquids might migrate from pole to pole.

 

Among the things that remain uncertain is exactly how the methane in Titan's atmosphere is being replenished, since it's broken down over time by sunlight. Scientists see some evidence of volcanism, with methane-laden water as the "lava," but a definitive detection remains elusive.

 

Cassini's long-term observations could still provide clues. Researchers have been watching for summer rain clouds to appear at the north pole, as their models predicted. Cassini observed rain clouds at the south pole in southern summer in 2004. But so far, clouds at high northern latitudes have been sparse.

 

"The atmosphere seems to have more inertia than most models have assumed. Basically, it takes longer than we thought for the weather to change with the seasons," said Elizabeth Turtle, a Cassini imaging team associate at Johns Hopkins Applied Physics Laboratory, Laurel, Maryland.

 

The sluggish arrival of northern summer clouds may match better with models that predict a global reservoir of methane, Turtle said. "There isn't a global reservoir at the surface, so if one exists in the subsurface that would be a major revelation about Titan." This points to the value of Cassini's long-term monitoring of Titan's atmosphere, she said, as the monitoring provides data that can be used to test models and ideas.

 

Results from the Last Close Pass

 

Cassini made its last close flyby of Titan on April 22. That flyby gave the spacecraft the push it needed to leap over Saturn's rings and begin its final series of orbits, which pass between the rings and the planet.

 

During that flyby, Cassini's radar was in the driver's seat -- its observation requirements determining how the spacecraft would be oriented as it passed low over the surface one last time at an altitude of 608 miles (979 kilometers). One of the priorities was to have one last look for the mysterious features the team dubbed "magic islands," which had appeared and then vanished in separate observations taken years apart. On the final pass there were no magic islands to be seen. The radar team is still working to understand what the features might have been, with leading candidates being bubbles or waves.

 

Most interesting to the radar team was a set of observations that was both the first and last of its kind, in which the instrument was used to sound the depths of several of the small lakes that dot Titan's north polar region. Going forward, the researchers will be working to tease out information from these data about the lakes' composition, in terms of methane versus ethane.

 

As Cassini zoomed past on its last close brush with Titan, headed toward its Grand Finale, the radar imaged a long swath of the surface that included terrain seen on the very first Titan flyby in 2004. "It's pretty remarkable that we ended up close to where we started," said Wall. "The difference is how richly our understanding has grown, and how the questions we're asking about Titan have evolved."

 

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. JPL designed, developed and assembled the Cassini orbiter.

Quelle: NASA

 

 

 

 

 

 

 


Tags: Cassini Spacecraft Raumfahrt - Cassini Grand Finale Around Saturn -Update-3 

1352 Views

Sonntag, 13. August 2017 - 22:00 Uhr

Astronomie - Wissenschaftler helfen, Neptuns chemisches Make-up vorherzusagen

13.08.2017

Scientists help predict Neptune’s chemical make-up

Scientists have helped solve the mystery of what lies beneath the surface of Neptune – the most distant planet in our solar system.

A new study sheds light on the chemical make-up of the planet, which lies around 4.5 billion kilometres from the sun.

Frozen worlds

Extremely low temperatures on planets like Neptune – called ice giants – mean that chemicals on these distant worlds exist in a frozen state, researchers say. 

Frozen mixtures of water, ammonia and methane make up a thick layer between the planets’ atmosphere and core – known as the mantle. 

However, the form in which these chemicals are stored is poorly understood.

Computer simulations

Using laboratory experiments to study these conditions is difficult, as it is very hard to recreate the extreme pressures and temperatures found on ice giants, researchers say.

Instead, scientists at Edinburgh ran large-scale computer simulations of conditions in the mantle. 

By looking at how the chemicals there react with each other at very high pressures and low temperatures, they were able to predict which compounds are formed in the mantle.

Computer models are a great tool to study these extreme places, and we are now building on this study to get an even more complete picture of what goes on there.

Dr Andreas HermannCentre for Science at Extreme Conditions

Chemical compound

The team found that frozen mixtures of water and ammonia inside Neptune – and other ice giants, including Uranus – likely form a little-studied compound called ammonia hemihydrate.

The findings will influence how ice giants are studied in future and could help astronomers classify newly discovered planets as they look deeper into space.

The study, published in the journal Proceedings of the National Academy of Sciences, was supported by Engineering and Physical Sciences Research Council. 

The work was carried out in collaboration with scientists at Jilin University, China.

This study helps us better predict what is inside icy planets like Neptune. Our findings suggest that ammonia hemihydrate could be an important component of the mantle in ice giants, and will help improve our understanding of these frozen worlds.

Dr Andreas HermannCentre for Science at Extreme Conditions
Quelle: University of Edinburgh

Tags: Astronomie - Wissenschaftler helfen, Neptuns chemisches Make-up vorherzusagen 

528 Views

Sonntag, 13. August 2017 - 07:40 Uhr

Astronomie - China’s astronomers hope to leap from the 4-meter Large Sky Area Multi-Object Fiber Spectroscopic Telescope to a new 12-meter telescope.

13.08.2017

China’s astronomers hope to leap from the 4-meter Large Sky Area Multi-Object Fiber Spectroscopic Telescope to a new 12-meter telescope.

Spat over design of new Chinese telescope goes public 

A deep division among Chinese astronomers over the design of a proposed 12-meter telescope broke into public view this week as statements from competing camps went viral on social media.

The dispute centers on whether to adopt a technically ambitious four-mirror design proposed by optical engineers or a conventional three-mirror option favored by astronomers. The stakes are high. It will be China’s largest optical telescope and serve as the workhorse observational facility for several generations.

In a 4 August letter to the Chinese Academy of Sciences (CAS), Jiansheng Chen, an astronomer at Peking University in Beijing, notes that currently the largest Chinese-built scopes are a 2.16-meter general purpose instrument and the 4-meter Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) that is dedicated to surveys. LAMOST “is not very successful,” he adds, noting that its performance doesn’t match that of the 2.5-meter Sloan Digital Sky Survey telescope at Apache Point Observatory in New Mexico. “You can imagine how much risk there is in leaping from this foundation to 12 meters!” Chen writes in the letter that was posted on WeChat, a popular Chinese social media platform. 

Chen miscalculates LAMOST’s aperture, counter Xiangqun Cui, the instrument’s chief engineer who is at Nanjing Institute of Astronomical Optics & Technology, and Dingqiang Su, an astronomer at Nanjing University, in a joint WeChat response posted 8 August. They write that in terms of its engineering, the aperture is equivalent to almost 8 meters, thus it wouldn't be a great leap to 12.

Chen, Cui, and Su are all prestigious CAS academicians, adding spice to the acrimonious exchange, which is just the latest skirmish in an ongoing battle.

Cui and her colleagues are behind the four-mirror design, which has a primary plus three secondary mirrors and relies on what they call an SYZ optical system, named using the initials of three designers who pioneered the scheme on the 2.16-meter telescope. A team from Huazhong University of Science and Technology in Wuhan has proposed a more conventional Ritchey-Chrétien design that has a primary plus two secondary mirrors. They claim this simpler approach provides better resolution in the central field of view, and “generally better scientific performance.”

In April, an international committee convened by CAS’s Center for Astronomical Mega-Science, which is responsible for the project, reviewed the competing designs and recommended the three-mirror option. On 10 July, Cui organized her own review committee that picked the SYZ design as better. Cui’s panel “leaned toward one side,” Chen says. And one member says that the three-mirror design was not sufficiently presented, partly because no one from the Huazhong team was there. Cui and Su explain in their open letter that a member of their own group who knows it well introduced the Huazhong design. “Members were repeatedly reminded they could abstain from voting,” they write. One-third of the 21 committee members did abstain.

Meanwhile, to date, more than 130 young astronomers have signed an open letter to the astronomical community urging that the recommendations of the international panel be respected.

The fundamental disagreement, according to Chen, is “whether a large science project should be technically or scientifically oriented.” Cui and Su say the choice is between incorporating “rapidly developing new technologies” that ensure a long life for the facility, or “simply replicating a 10-meter telescope built 30 years ago.”

This week, more than 800 astronomers are attending the annual meeting of the Chinese Astronomical Society in Xinjiang. The 12-meter telescope battle is not on the program. The society “doesn’t want to cause embarrassment,” says one attendee who adds there is sure to be “a lot of [discussion] in private.”

Quelle: AAAS


Tags: Astronomie - China’s astronomers hope to leap from the 4-meter Large Sky Area Multi-Object Fiber Spectroscopic Telescope to a new 12-meter telescope. 

505 Views

Sonntag, 13. August 2017 - 07:35 Uhr

Astronomie - Totale Sonnenfinsternis am 21. August 2017 über USA -Update-1

25.07,2017

sofi-2017-usa

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Chasing the Total Solar Eclipse from NASA’s WB-57F Jets

For most viewers, the Aug. 21, 2017, total solar eclipse will last less than two and half minutes. But for one team of NASA-funded scientists, the eclipse will last over seven minutes. Their secret? Following the shadow of the Moon in two retrofitted WB-57F jet planes. 

 

Amir Caspi of the Southwest Research Institute in Boulder, Colorado, and his team will use two of NASA’s WB-57F research jets to chase the darkness across America on Aug. 21. Taking observations from twin telescopes mounted on the noses of the planes, Caspi will ­­­­­capture the clearest images of the Sun’s outer atmosphere — the corona — to date and the first-ever thermal images of Mercury, revealing how temperature varies across the planet’s surface.

 

“These could well turn out to be the best ever observations of high frequency phenomena in the corona,” says Dan Seaton, co-investigator of the project and researcher at the University of Colorado in Boulder, Colorado. “Extending the observing time and going to very high altitude might allow us to see a few events or track waves that would be essentially invisible in just two minutes of observations from the ground.”

For most viewers, the Aug. 21, 2017, total solar eclipse will last less than two and half minutes. But for one team of NASA-funded scientists, the eclipse will last over seven minutes. Their secret? Following the shadow of the Moon in two retrofitted WB-57F jet planes. Amir Caspi of the Southwest Research Institute in Boulder, Colorado, and his team will use two of NASA's WB-57F research jets to chase the darkness across America on Aug. 21. Taking observations from twin telescopes mounted on the noses of the planes, Caspi will capture the clearest images of the Sun's outer atmosphere -- the corona -- to date and the first-ever thermal images of Mercury, revealing how temperature varies across the planet's surface.
Credits: NASA's Goddard Space Flight Center

 

The total solar eclipse provides a rare opportunity for scientists to study the Sun, particularly its atmosphere. As the Moon completely covers the Sun and perfectly blocks its light during an eclipse, the typically faint corona is easily seen against the dark sky. NASA is funding 11 science projects across America for scientists to take advantage of the unique astronomical event to learn more about the Sun and its effects on Earth’s upper atmosphere.

 

composite image of WB-57F planes and a solar eclipse
(Photo illustration) During the upcoming total solar eclipse, a team of NASA-funded scientists will observe the solar corona using stabilized telescopes aboard two of NASA’s WB-57F research aircraft. This vantage point provides distinct advantages over ground-based observations, as illustrated by this composite photo of the aircraft and the 2015 total solar eclipse at the Faroe Islands.
Credits: NASA/Faroe Islands/SwRI

The corona is heated to millions of degrees, yet the lower atmospheric layers like the photosphere — the visible surface of the Sun — are only heated to a few thousand degrees. Scientists aren’t sure how this inversion happens. One theory proposes that magnetic waves called Alfvén waves steadily convey energy into the Sun’s outer atmosphere, where it is then dissipated as heat. Alternatively, micro explosions, termed nanoflares — too small and frequent to detect individually, but with a large collective effect — might release heat into the corona.

 

WB-57F jet
One of the WB-57F jets is readied for a test run at NASA’s Johnson Space Center in Houston. The instruments are mounted under the silver casing on the nose of the plane.
Credits: NASA’s Johnson Space Center/Norah Moran

Due to technological limitations, no one has yet directly seen nanoflares, but the high-resolution and high-speed images to be taken from the WB-57F jets might reveal their effects on the corona. The high-definition pictures, captured 30 times per second, will be analyzed for wave motion in the corona to see if waves move towards or away from the surface of the Sun, and with what strengths and sizes.

 

“We see the evidence of nanoflare heating, but we don’t know where they occur,” Caspi said. “If they occur higher up in the corona, we might expect to see waves moving downwards, as the little explosions occur and collectively reconfigure the magnetic fields.”

 

In this way, nanoflares may also be the missing link responsible for untangling the chaotic mess of magnetic field lines on the surface of the Sun, explaining why the corona has neat loops and smooth fans of magnetic fields. The direction and nature of the waves observed will also help distinguish between competing models of coronal heating.

 

The two planes, launching from Ellington Field near NASA’s Johnson Space Center in Houston will observe the total eclipse for about three and a half minutes each as they fly over Missouri, Illinois and Tennessee. By flying high in the stratosphere, observations taken with onboard telescopes will avoid looking through the majority of Earth’s atmosphere, greatly improving image quality. At the planes’ cruising altitude of 50,000 feet, the sky is 20-30 times darker than as seen from the ground, and there is much less atmospheric turbulence, allowing fine structures and motions in the Sun’s corona to be visible.

 

Images of the Sun will primarily be captured at visible light wavelengths, specifically the green light given off by highly ionized iron, superheated by the corona. This light is best for showing the fine structures in the Sun’s outer atmosphere. These images are complementary to space-based telescopes, like NASA’s Solar Dynamics Observatory, which takes images primarily in ultraviolet light and does not have the capacity for the high-speed imagery that can be captured aboard the WB-57F.

 

Observations of Mercury will also be taken a half-hour before and after totality, when the sky is still relatively dark. These images, taken in the infrared, will be the first attempt to map the variation of temperature across the surface of the planet.

 

Mercury rotates much slower than Earth — one Mercurial day is approximately 59 Earth days — so the night side cools to a few hundred degrees below zero while the dayside bakes at a toasty 800 F. The images will show how quickly the surface cools, allowing scientists to know what the soil is made of and how dense it is. These results will give scientists insight into how Mercury and other rocky planets may have formed.

 

The images of the corona will also allow the team to search for a hypothesized family of asteroids called vulcanoids. Its thought these objects orbit between the Sun and Mercury, and are leftover from the formation of the solar system. If discovered, vulcanoids could change what scientists understand about planet formation.

Quelle: NASA

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Update: 5.08.2017

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Chasing the Total Solar Eclipse From Orbit

While millions will watch the August 21st total solar eclipse from the ground, the International Space Station crew will have an amazing view high overhead.

Umbra from the ISS

The umbra of the Moon as seen from the International Space Station during the March 29, 2006 total solar eclipse. 
NASA

Less than three weeks lie between us and the first total solar eclipse cross the contiguous United States in 38 years. If you're like us, you've already got a plan (and a backup plan) for the main event on Monday, August 21st. (Observers in eastern Europe,  Africa, and Asia won't miss out completely: they'll see the pre-show event, a partial lunar eclipse on Monday, August 7/8th.)

The path of the August 21st, 2017 total solar eclipse across the United States. 
Michael Zeiler / greatamericaneclipse.com

Humans in space will watch as well, as the International Space Station zips 250 miles above Earth's surface, orbiting the planet once every 93 minutes.

"Our flight team is tracking opportunities for astronauts onboard the station to photograph both the eclipse and the Moon's shadow on the planet," says Daniel Huot (NASA Johnson Space Center) "They have solar filters for photographing the eclipse itself and will have one opportunity to see the Moon's shadow.

 

Astronauts have witnessed solar eclipses from space before, starting with the partial solar eclipse caught by Gemini 12 on November 12, 1966. More recently, NASA astronaut (and amateur astronomer) Don Pettit captured a total solar eclipse over the Pacific in May 2012, and European Space Agency astronaut Samantha Chistoforetti nabbed the partial phase of the March 20, 2015, total solar eclipse over the Faroe Islands. NASA astronaut Randy Bresnik recently arrived aboard the ISS and is, like Pettit, also a skilled photographer who is up to the challenge.

Thus far, though, no one on the ISS has managed to “thread the needle,” with a view passing through the narrow umbra of a total solar eclipse. Such a view would, of course, be fleeting, as the ISS moves 17,000 mph from southwest to the northeast, while the umbra of the Moon crosses the U.S. on August 21st from the northwest to the southeast at speeds up to 1,400 mph near mid-eclipse.

ISS vs the eclipse

The first pass of the ISS during the eclipse at 16:41 UT (note: the inset shows the eclipsed Sun; the graphics are from the Sun's perspective. 
NASA/JSC

NASA currently plans on three opportunities to spy the eclipse during partial phases. The first pass will occur at 16:41 Universal Time (UT), just prior to the touchdown of the umbra over the Pacific at 16:49 UT, with partial phases of the eclipse already underway for western North America. ISS astronauts will see a 37% eclipsed Sun on this first pass.

The second pass of the ISS during the eclipse at 18:24 UT. 
NASA/JSC

On pass two at 18:24 UT, things could get interesting. Although the ISS will not pass through the umbra, it should be visible from the station as it races races across Illinois, Kentucky, and Tennessee near maximum totality. Mir cosmonauts managed to catch this kind of view during the total solar eclipse crossing Europe one saros cycle ago, on August 11, 1999.

The third pass of the ISS during the eclipse at 18:16 UT. 
NASA/JSC

Finally, the ISS crew will say goodbye to the eclipse as it departs Earth over the mid-Atlantic. This could provide an amazing opportunity to catch the “horns” of the eclipsed Sun setting behind the limb of the Earth, as the Sun fattens from 85% coverage to 27%.

At present, these times are approximate. The ISS is scheduled to perform an orbital boost on August 9th, and there's always the possibly of an unscheduled Debris Avoidance Maneuver (DAM) over the next few weeks.

“Flight controllers are still finalizing the details and identifying windows that might give a view of the Sun during the eclipse,” says Huot. ISS crew will be shooting the Sun out the cupola window using DSLRs and filter-covered lenses.

Catching a Transit of the ISS on Eclipse Day

GOES eclipse

GOES-10 sees the shadow of the Moon cross the Earth on February 26, 1998. 
NASA / GSFC / NOAA

As the ISS passes overhead, there's also a good chance to nab the station transiting the partially eclipsed Sun during those first two passes. Renowned astrophotographer Thierry Legault captured the ISS crossing a partially eclipsed Sun from Oman on January 4, 2011.

This kind of shot takes some planning, as you have to be right along the precise path of the transit at the right time. You'll need the ability to shoot at a high frame rate or video with a properly filtered camera rig equipped with a zoom of at least 400 mm or better, to produce a good-sized disk of the Sun. ISS transits of the Sun or Moon are quick, often lasting less than 1 second. I like to have an accurate audible time hack via WWV Radio on shortwave AM playing in the background as well to know when to begin shooting.

CalSky is your best bet for precise transit predictions leading up to the eclipse. Keep in mind, the orbit of the ISS changes over time due to periodic boosts and atmospheric drag, so check those pass predictions within 48 hours of eclipse day.

Other missions may see the eclipse from space as well. The joint JAXA/NASA mission Hinode observes the Sun from a low-altitude orbit, as does the European Space Agency's Proba 2. Full-disk Earth-observing satellites such as DSCOVR, Himawari 8 and GOES 15 also typically nab the umbra of the Moon sliding across the face of Earth as well.

Another big question is the exact shape of the corona — the pearly-white aura of plasma surrounding the Sun seen only during totality — on eclipse day. We're inside the one Carrington solar rotation (that is, one rotation for 26#176; solar latitude, a period of 27.3 Earth days), and the National Solar Observatory Integrated Synoptic Program recently released a prediction for what shape the corona should take come eclipse day:

NASA will also employ a pair of converted WB-57 bombers to chase totality's shadow. In addition to observing the solar corona, the aircraft will take infrared images of Mercury pre- and post-totality, as well as sweep the skies near the eclipsed Sun for tiny Vulcanoid asteroids.

The big advantage to taking to the air and space, of course, is not having to worry about eclipse-day weather. We should start seeing the first long-range forecasts for those of us on the ground late next week, and we'll be watching Clear Sky ChartsSkippy Sky and NOAA models the weekend prior.

Remember, you don't need clear skies, just a clear view of the Sun during those precious minutes of totality!

Quelle: Sky&Telescope

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Update: 8.08.2017

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The Great American Eclipse Is 2 Weeks Away. Are You Ready?

watchingsolareclipseta-6134775

The Aug. 21 total solar eclipse will sweep across the continental U.S., beginning in Oregon and ending in South Carolina. The last time an eclipse touched both American coasts was in 1918. Eclipse enthusiasts say this phenomenon is one of the most spectacular sights in nature. As a sort of celestial preview, the moon will pass through part of Earth's shadow in a partial lunar eclipse today (Aug. 7). 

Skywatchers throughout the U.S. will be able to witness a partial solar eclipse on Aug. 21, when the moon covers less than 100 percent of the sun's disk. But only skywatchers inside the path of totality will see the incredible phenomenon of a total solar eclipse. Wherever you will be, it's a good idea to have solar viewing glasses on hand. Or, you can build your own pinhole camera to watch the moon's progress across the sun.

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You can use this interactive eclipse map to find out exactly where totality will be visible, as well as when totality will occur at different locations inside the path. Totality will last for less than 3 minutes depending on how close you are locatedto the center line, so make sure you are looking skyward at the right time!

 If you plan on traveling to see totality, be aware that experts are expecting nightmarish traffic conditions. Plan for extra time to reach your destination. Many cities and towns along the path of totality are planning eclipse-related events that could cause additional traffic delays. Research your destination ahead of time to find out where to park and where to observe the eclipse.

With two-thirds of Americans living within a day's drive of the eclipse, some eclipse experts have anticipated that the weekend leading up to the August eclipse will see more travelers in the air, on the rails and on the road than any other time in 2017. That could present serious problems for those viewing the eclipse, even if they don't have to travel to see it. And people who live inside the eclipse path but choose to miss the once-in-a-lifetime event will not be spared.

"There will hopefully be less bloodshed, but zombies don't need regular food, or sleep, or toilets," Speck said. Eclipse spectators, on the other hand, need all those things. 

A total solar eclipse occurs when the moon completely blocks the disk of the sun. While partial solar eclipses are common, with two to five occurring around the world each year, a total solar eclipse happens somewhere on Earth only about once every 18 months. The last total solar eclipse touched the continental United States in 1979, and the last to cross from ocean to ocean occurred in 1918.

The August eclipse will pass through 14 states and five state capitals. During the partial phase, as the moon takes a bite out of the sun, observers should use eclipse glasses or a pinhole camera to watch the eclipse, as should those only able to observe a partial eclipse. 

Totality (the period in which the disk of the sun is completely hidden) will last less than 3 minutes, but can be a truly stunning sight. After the body of the sun is completely blocked and the vicinity is cloaked in darkness, observers can remove their glasses. The dancing tendrils of the sun's outer atmosphere, usually outshone by its brighter body, will become visible. 

REMEMBER: Looking directly at the sun, even when it is partially covered by the moon, can cause serious eye damage or blindness. NEVER look at a partial solar eclipse without proper eye protection. See our complete viewing guide to find out how to view the eclipse safely.

As the final days wind down to the eclipse, make sure you have your eclipse glasses. Sunglasses — even multiple pairs — are insufficient for viewing an eclipse. A pinhole viewer can also allow you to safely watch the event without damaging your vision.

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"Many cities along the path of totality have been preparing for this and [are setting] up multiple observing sites with safe solar viewing gear," Paul Sutter, a researcher and outreach coordinator at Ohio State University (and a Space.com contributor), said in an email.

Don't despair if you can't make it to one of these sites. 

"Just go somewhere else," Sutter said. "A park, a parking lot, your back yard. You just need a good view of the sky and you're golden."

While the eclipse itself is brief, it may be worth coming early for the science talks that may occur. 

"If you can, I highly recommend making a whole day out of it," Sutter said.

August 21 could be the busiest travel day of the year, as people journey into the path of the total solar eclipse.
Credit: Scott Olson/Getty Images 

While 12 million people live within the path of totality, another 200 million people live within a day's drive of the eclipse. How many intend to travel to see the eclipse remains unknown. Michael Zeiler, an eclipse cartographer, conservatively estimates that between 1.85 million and 7.4 million people may journey experience the total eclipse. 

If you are planning to travel for the eclipse, you've hopefully already made hotel reservations. Most — if not all — of the hotel rooms along the eclipse path are filled, as serious eclipse hunters have been planning for the event for well over a year. Alternative housing arrangements, such as campsites or rooms in private homes, may still be available. But even if you are planning to stay with a friend, expect problems.

That's because the population of cities along the eclipse path is expected to double in the days around the event, Speck said, a rise that could trigger a host of unexpected problems.

"No town or city has the capacity to house so many visitors in hotels; nowhere has enough restaurants to feed such a huge crowd," she said. "Are there enough bathrooms? Probably not."

Folks who live along the path — whether they plan to see the eclipse or not — should prepare much like they would before a major storm. Speck advises folks to stock their fridges and fill up their cars with gas, "because the chances are that neither supermarkets nor gas stations will be sufficiently supplied." That means if you're crashing with friends or family, don't bank on eating out or parking downtown. [How to Survive the Total Solar Eclipse of 2017]

 

 
 
 
 
 

 

Speck proposed that communities can prepare by having gas stations fill up extra tanks and supermarkets keep refrigerated trucks on hand for extra storage. 

"Maybe restaurants could do special reduced menus to get the crowd thru quicker, maybe they could hire extra staff just for the event." 

Businesses aren't the only ones who need to prepare. 

"Maybe churches could host food lines and make some money whilst helping to prepare for the crowds," she said.

While traffic leading up to the eclipse will likely be bad — Speck suggested at least doubling the anticipated travel time between destinations — it could be even worse during the event. An unexpected patch of clouds across a clear sky could send people to their cars in search of a clear view, causing even more problems.

Logistical problems aside, Speck is looking forward to the eclipse. 

"It is such an all-encompassing experience," she said.

Sutter, who will be leading an event in Nashville, Tennessee, is equally enthusiastic.

"I'm really looking forward to sharing this spectacle with my group, and really sharing it with the entire country," he said. "Nature is putting on a free show for us, and it's something we all get to enjoy!"

Editor's note: Space.com has teamed up with Simulation Curriculum to offer this awesome Eclipse Safari app  to help you enjoy your eclipse experience. The free app is available for Apple and Android, and you can view it on the web

This article was updated to show that Angela Speck is a researcher at the University of Missouri, not the University of Maryland.

Quelle: SC

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Update: 10.08.2017

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NMSU students help NASA livestream total solar eclipse

 

LAS CRUCES, N.M. (KRQE) – It’s going to be a rare sight to see, and a group from New Mexico is going to be part of a project NASA is sponsoring to livestream aerial videoof the total solar eclipse as it crosses the United States.

It has been coined the “Great American Eclipse.” It will be a total eclipse of the sun, visible from coast to coast for the first time in 99 years.

The moon will move in front of the sun casting a shadow on the ground on Monday, August 21, causing total darkness if you’re in its path from Oregon to South Carolina.

For those who aren’t, like us here in New Mexico, NASA is sponsoring a project to livestream aerial video of it at http://eclipse.stream.live/ 

Two students and a senior research scientist from the New Mexico Space Grant Consortium at New Mexico State University make up one of more than 50 teams that will travel to different points along the path to make it happen.

“We’re just very excited to be a part of it, and this is a once in a lifetime opportunity,” said Norann Calhoun, a chemical engineering major at NMSU.

The group will leave NMSU on Thursday, August 17 to drive to Homestead National Monument of America in Nebraska.

That’s where they’ll launch a roughly 8-foot tall balloon 100,000 feet up in the sky.

“It should take about two hours to get to 100,000 feet and so we’re going to have to kind of time that with when the eclipse starts,” said Sten Hasselquist, an astronomy doctoral student.

They’re expecting the eclipse to last about two-and-a-half minutes.

Cameras equipped with GPS will be attached to the balloon so that when it’s over, they can cut the balloon down and retrieve the equipment wherever it lands.

They could be streaming for a huge crowd.

“It’s going to be in the millions,” Senior Research Scientist Paulo Oemig said.

Each balloon will also carry a highly-resilient bacteria to the stratosphere.

“As it reaches that high altitude, it will simulate the environment of Mars since there’s no really an ozone layer strong enough to protect it from ultra violet radiation and really low temperatures and really lack of water,” Oemig said.

Quelle: KRQE NEWS 13

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Citizen scientists chase total solar eclipse

Non-scientists are being recruited to collect data on everything from the Sun’s outer atmosphere to animal behaviour.

 

Babak Tafreshi/NGC

The Sun’s corona becomes visible during an eclipse.

Fred Isberner is a retired healthcare professor in Carbondale, Illinois. But on 21 August, the 69-year-old will be collecting data about the Sun’s superheated outer atmosphere during a total solar eclipse. Isberner is one of thousands of people across the United States who plan to gather data during the event. Their combined efforts will be one of the largest, one-off citizen-science efforts yet.

“It absolutely has the potential to be the biggest,” says Scott McIntosh, director of the National Center for Atmospheric Research’s High Altitude Observatory in Boulder, Colorado.  

Total solar eclipses occur about once every 18 months, but they often pass over remote areas such as the ocean. The 21 August eclipse is rare because it will be visible over a heavily populated landmass — the continental United States. About 12 million people live in the path of totality, which stretches from Oregon to South Carolina. Scientists and volunteers plan to take advantage of the situation to gather data and encourage the public to participate in research.

Star gazers

One of the larger efforts is the Eclipse Megamovie Project. The team behind it is inviting anyone with a camera, telescope or smartphone to submit images of the eclipse to an app. Data collected by the project, co-led by McIntosh, will allow researchers to study the ‘diamond ring effect’: a period when sunlight leaks through a valley on the Moon prior to and just after totality, resembling the diamond on a ring. Analysing how this effect changes during the eclipse could help scientists to measure the size of the Sun more precisely.

The project that Isberner is part of — Citizen Continental-America Telescopic Eclipse (Citizen CATE) — involves 68 teams of volunteer stargazers along the path of totality. They will capture images of the eclipse using identical telescopes to get a close, continuous look at the corona, the Sun’s outermost atmosphere. It is a region people normally do not see owing to the Sun's brightness. Researchers hope to spot features including plumes, streamers and loops.

If they are successful, the data could provide insights about this poorly studied region of the Sun, says Matt Penn, a solar astronomer at the National Solar Observatory in Tucson, Arizona, and leader of the Citizen CATE project. Penn’s team will analyse the information and compile the images into a 90-minute timelapse. “No one has taken a 90-minute sequence of this part of the solar atmosphere before”, he says.

Coming home to roost

Not every citizen-science effort will focus on the heavens, however. A project called Life Responds will ask people to record what animals do during the eclipse. Volunteers can submit their observations on the iNaturalist app.

Life Responds is the brainchild of Elise Ricard, a public programmes supervisor at the California Academy of Sciences in San Francisco, who noticed that birds stopped singing during a 2012 eclipse in Australia. “It wasn’t just us on the beach enjoying the eclipse,” Ricard says. “Animal life was responding.”

There is a lot of anecdotal evidence of odd animal behaviour during an eclipse, but research on it is sparse, says Andrew Fraknoi, a Life Responds adviser and retired astronomy professor at Foothill College in Los Altos Hills, California.

Stories of unusual behaviour during a solar eclipse include chickens returning to their roosts, llamas surrounding a group of people during the event and whales and dolphins surfacing around a boat minutes before totality.

The data collected by Life Responds is not currently destined for a scientific study. But Ricard hopes that the observations will inspire future research on animal behaviour during eclipses.

The sounds of an eclipse

Other projects will keep an ear out on 21 August. The Eclipse Soundscapes project wants people to collect audio of wildlife in urban and rural settings during the eclipse. The information could have potential applications for anthropological or biological studies, says project leader Henry Winter, an astrophysicist at Harvard University in Cambridge, Massachusetts.

His primary goal, however, is to create an app that pairs sound and vibrations to deliver an eclipse experience to blind people. The idea came to Winter when he noticed that some solar eclipse museum displays only included one label written in braille for the visually impaired.

Like Winter, the scientists leading these projects emphasize the importance of including non-researchers in scientific endeavours. “It gives people the sense that they can contribute to science,” says Fraknoi, who is also helping with Citizen CATE.

This is especially true for students. “It will get kids outside of the classroom and give them the hands-on ability to explore science instead of reading about it in a textbook,” says Janet Jorgensen, a former prinicpal at Harlem Junior High School in Harlem, Montana. She will be in Jay Em, Wyoming, along with two teachers and a student from her former school collecting data for Citizen CATE.

The excitement of doing science is a sentiment Isberner, the first Citizen CATE volunteer, can get behind. “Proves that an old guy like me can be trained without any experience in astroimaging and succeed,” he says.

Quelle: nature

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Update: 13.08.2017

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Space station crew to get three shots at solar eclipse

The International Space Station's crew will enjoy views of the Aug. 21 solar eclipseduring three successive orbits, giving the astronauts a unique opportunity to take in the celestial show from 250 miles up as the moon's shadow races across from the Pacific Ocean and the continental United States before moving out over the Atlantic.

"Because we're going around the Earth every 90 minutes, about the time it takes the sun to cross the U.S., we'll get to see it three times," Randy Bresnik said Friday during a NASA Facebook session. "The first time will be just off the West Coast, we'll actually cross the path of the sun, and we'll have (a partial) eclipse looking up from the space station."

For the station crew, the first partial eclipse opportunity will begin at 12:33 a.m. EDT (GMT-4) and end 13 minutes later.

Floating in the European Columbus laboratory module, Bresnik showed off a solar filter shipped up to the station earlier, saying "we've got specially equipped cameras that'll have these solar filters on them that allow us to take pictures of the sun. That's going to be pretty neat, we'll have a couple of us shooting that."

081117-bresnik.jpg
Caption

Space station astronaut Randy Bresnik shows off a solar filter that will be used by the crew during multiple opportunities to photograph the Aug. 21 solar eclipse from their perch 250 miles up.

 NASA TV

One orbit later, the station will cross the path of the eclipse in the extreme northwest following a trajectory that will carry the lab over central Canada on the way to the North Atlantic. From the station's perspective, 44 percent of the sun will be blocked in a partial eclipse. But the crew will be able to see the umbra, where the eclipse is total, near the southern horizon.

"We'll be north of Lake Huron in Canada when we'll be able to see the umbra, or the shadow of the eclipse, actually on the Earth, right around the Tennessee-Kentucky (area), the western side of both those states," Bresnik said. "That'll be an opportunity for us to take video, and take still pictures and kind of show you from the human perspective what that's going to look like."

081117-iss-map2.jpg
Caption

During the second of three successive orbits, the space station crew, passing just south of Hudson Bay, will have a chance to see and photograph the moon's shadow as it moves across western Kentucky and northwestern Tennessee some 1,100 miles away.

 NASA

The umbra, defining the 70-mile-wide shadow where the sun's disk will be completely blocked out, will be at its closest to the space station at 2:23 p.m. The moon's shadow will be about 1,100 miles away from the lab complex, but from their perch 250 miles up, the astronauts should be able to photograph the dark patch as they race along in their orbit.

"And then the third pass is actually just off the East Coast," Bresnik said. "We'll come around one more time and from the station side we'll see about an 85 percent eclipse of the sun looking up (at 4:17 p.m.). So we should be able to get really neat photos, with our filters, of the sun being occluded by the moon."

NASA plans to provide four hours of eclipse coverage, starting at noon EDT, on the agency's satellite television channel, in web streams and via social media, including Twitter, Instagram and Facebook.

"We have a lot of options to share all this," Bresnik told a Facebook questioner. "It's U.S. taxpayer dollars. ... You're paying us to take these pictures, and they go to you. They're free to everybody, and you can access them from the NASA website."

Quelle: CBS News


Tags: Astronomie - Totale Sonnenfinsternis am 21. August 2017 über Clarksville,Tennessee (USA) Update-1 

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Sonntag, 13. August 2017 - 07:30 Uhr

Astronomie - Shadow Bands Are a Solar Eclipse Mystery (and Not Everyone Sees Them)

13.08.2017

Shadow Bands Are a Solar Eclipse Mystery (and Not Everyone Sees Them)
This historic drawing depicts shadow bands, a hard-to-spot phenomenon that sometimes appears during solar eclipses. 
Credit: Courtesy of Sky and Telescope Magazine

On Aug. 21, as most readers certainly know by now, the shadow of the moon will sweep down from space and slide across the surface of the Earth, bringing a total solar eclipse to parts of the contiguous United States for the first time in a generation. The highlight of totality for many will be the opportunity to view the incredible solar corona — the twisted outer atmosphere that reveals the presence of the sun's active magnetic field — as well as seeing stars and planets pop into view during the daytime. But there is another unusual phenomenon that is visible only when the sun has narrowed to just a filament of light: shadow bands.

Among the eerie phenomena that can accompany an eclipse of the sun, shadow bands are perhaps the most unusual. These mysterious gray ripples are sometimes seen flitting over the ground within several minutes of totality (the period when the sun's disk is fully concealed by the moon). Initially, the bands appear faint and jumbled; but as totality draws near, they become more organized, their spacing decreases to an inch or two and they become more visible. After totality ends, the pattern reverses: the bands reappear and become progressively fainter and more disorganized until they finally disappear. [How to View a Solar Eclipse Without Damaging Your Eyes]

And yet at a particular eclipse, observers at different locations along the eclipse path will see quite different shadow band effects, with people at some locations reporting almost unobservable bands while others seeing them quite distinctly. At some eclipses the bands are quite vivid and conspicuous, while at other eclipses they will be very faint or not visible at all. 

 

Nobody can state with certainty as to when shadow bands were first noted. According to George F. Chambers in his book "The Story of Eclipses" (Appleton, 1902), the shadow-band phenomenon was reported at the eclipse of July 8, 1842. By 1878 in Colorado, observers were prepared for the appearance of the "diffraction bands." Possibly the reason for the paucity of shadow-band observations before the mid-19th century is that so many viewers were concentrating their gaze upward in those final exciting few minutes rather than looking down!

 

 

Shadow bands are also very difficult to photograph and the reason is obvious: The bands usually occur when only about 1 percent (or less) of the sun remains uncovered by the moon, so only a few tenths of a percent of normal sunlight is left, so the contrast is very low. The typical speed of the bands along the ground is about 10 feet per second, and as they are generally only an inch or two wide, they become blurred and washed out when attempts are made to photograph or video them. 

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These successive images, captured during a solar eclipse by Wolfgang Strickling, show changing shadow bands.

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There is also a physiological reason why shadow bands are unrecognized in most photographs. The bands are much easier to see when they are in motion than when stationary, as this simple experiment shows. Hold a pencil horizontally over a sheet of paper that is illuminated by an overhead light. Slowly raise the pencil until you can no longer discern its shadow. Now move the pencil from side to side — the shadow suddenly becomes visible again, with about as much contrast as a typical shadow band. The pencil must be raised much higher above the paper to make the moving shadow invisible.  

Over the last 175 years, a variety of proposals have been forwarded to try to explain what shadow bands are. One of the first explanations was that the bands are very high-order fringes of a single-slit diffraction pattern (hence the term "diffraction bands"). This pattern is created by waves of light passing through a thin slit in a solid surface, creating one dark stripe in the middle and subsequently lighter stripes to each side. Then in 1924, Guido Horn-D'Arturo suggested the bands were overlapping pinhole images of the sun formed by spriragli, or gaps in the Earth's upper atmosphere.

But the most probable explanation seems to be a meteorological effect produced by the last of the sun’s rays being distorted by Earth's turbulent atmosphere; this same effect disturbs the light from distant stars, causing them to appear to twinkle. A star’s light is disturbed because, for all intents and purposes, it is nothing more than a point source of light in our sky. On the other hand, bright naked-eye planets such as Venus and Jupiter are not point sources but subtend to a much larger size. Thus, they rarely, if ever, appear to twinkle even when very near to the horizon. Of course, the sun and moon do not twinkle at all. 

However, during a solar eclipse, as the sun’s disk is reduced to a very narrow "filament" of light, each point along the filament should appear to twinkle like a star. Thus, shadow bands might be the net result of light coming from each shimmering point. Some believe that the worse the conditions are for telescopic viewing (because of atmospheric disturbances), the better the shadow bands. [First Time Seeing a Total Solar Eclipse? Check Out This Video from NASA]

In the 20th century, two "vintage" years stand out so far as shadow-band visibility is concerned. The first case is the eclipse of Jan. 24, 1925. Since this event came a few days after a heavy snowfall for the Northeast United States, shadow bands were readily seen upon the fresh snow by most eclipse watchers. Meteorologist Edward Brooks who observed this eclipse from Groton, Connecticut, noted in 1978: "The snow offered the ground offered the best backdrop for viewing the eerie fleeting shadow bands at any of the nine total eclipses I have gone to."

At the eclipse of March 7, 1970, which nearly paralleled the U.S. East Coast, many shadow-band sightings were recorded. To astronomer Glenn Schneider, watching from Greenville, North Carolina, the shadow bands resembled "jail bars."

Even outside the totality path, shadow bands can sometimes be observed. For instance, from Hyderabad, India, in 1980, where a partial eclipse covered more than 99 percent of the sun, a person who was among a group of eclipse watchers was heard to suddenly yell, "There’s fire on the ground!" But what he was witnessing was a sensational display of shadow bands. Not knowing at first what they were, they were described as "flames leaping 6 to 10 feet off the ground."  

Interestingly, I have been to 11 total eclipses, yet my only view of shadow bands came during an annular eclipse (when a ring of the sun's disk remains visible around the moon). On May 30, 1984, from Greenville, South Carolina, for about 90 seconds before and after the annular phase I caught sight of very weak smoky bands that displayed little movement but appeared to shimmer, resembling sunlight passing over a radiator or ripples of sunshine at the bottom of a breeze-stirred pool. 

To view shadow bands, many people will stretch a large white sheet on the ground. The best way to try to see them is to use a strongly backscattering surface, such as a glass-beaded projection screen that will improve image brightness, placed perpendicular to the rays of the sun. Start watching about 5 minutes before totality. As soon as you see the bands, note the time of appearance, and then the general direction in which they are moving by positioning a rod on the screen parallel to the direction of motion. Leave the rod in the position placed until after the end of totality, when the direction can be determined at leisure. You might want to have a second screen and rod prepared to observe the phenomenon just after totality (if it should appear). Estimate the width of the bands and the distance between the crest of the waves, how fast they are moving and whether they come singly or in groups.  

It also seems that the most intense bands are seen in warm, dry areas and not from coastal areas or from shipboard. This would seem to suggest that for the upcoming eclipse you would be more likely to see shadow bands from Casper, Wyoming, or St. Joseph, Missouri, as opposed to Lincoln City, Oregon, or Charleston, South Carolina.

Good luck in planning your observations and carrying them out!

Quelle: SC


Tags: Astronomie - Shadow Bands Are a Solar Eclipse Mystery (and Not Everyone Sees Them) 

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Samstag, 12. August 2017 - 23:00 Uhr

Raumfahrt - ISS-ALLtag: New Mission Going to the Space Station to Explore Mysteries of Cosmic Rain

12.08.2017

A new experiment set for an Aug. 14 launch to the International Space Station will provide an unprecedented look at a rain of particles from deep space, called cosmic rays, that constantly showers our planet. The Cosmic Ray Energetics And Mass mission destined for the International Space Station (ISS-CREAM) is designed to measure the highest-energy particles of any detector yet flown in space.

CREAM was originally developed as a part of NASA's Balloon Program, during which it returned measurements from around 120,000 feet in seven flights between 2004 and 2016.

Meet Cosmic Ray Energetics And Mass for the International Space Station (ISS-CREAM), an experiment designed to provide an unprecedented look at cosmic ray particles approaching energies of 1,000 trillion electron volts (1 PeV). ISS-CREAM detects these particles when they slam into the matter making up its instruments. They can distinguish electrons, protons and atomic nuclei as massive as iron as they crash through the detector stack.


"The CREAM balloon experiment achieved a total sky exposure of 191 days, a record for any balloon-borne astronomical experiment," said Eun-Suk Seo, a professor of physics at the University of Maryland in College Park and the experiment's principal investigator. "Operating on the space station will increase our exposure by over 10 times, taking us well beyond the traditional energy limits of direct measurements."

Technicians lower ISS-CREAM into a chamber that simulates the space environment during system-level testing at NASA's Goddard Space Flight Center in summer 2015.
Technicians lower ISS-CREAM into a chamber that simulates the space environment during system-level testing at NASA's Goddard Space Flight Center in summer 2015.Credits: University of Maryland Cosmic Ray Physics Laboratory


Sporting new instruments, as well as refurbished versions of detectors originally used on balloon flights over Antarctica, the refrigerator-sized, 1.4-ton (1,300 kilogram) ISS-CREAM experiment will be delivered to the space station as part of the 12th SpaceX commercial resupply service mission. Once there, ISS-CREAM will be moved to the Exposed Facility platform extending from Kibo, the Japanese Experiment Module.

The ISS-CREAM payload was delivered to NASA's Kennedy Space Center in August 2015. The experiment is shown wrapped in plastic layers used to protect its sensitive electronics during shipment.
The ISS-CREAM payload was delivered to NASA's Kennedy Space Center in August 2015. The experiment is shown wrapped in plastic layers used to protect its sensitive electronics during shipment.Credits: University of Maryland Cosmic Ray Physics Laboratory


From this orbital perch, ISS-CREAM is expected to study the "cosmic rain" for three years — time needed to provide unparalleled direct measurements of rare high-energy cosmic rays.

At energies above about 1 billion electron volts, most cosmic rays come to us from beyond our solar system. Various lines of evidence, including observations from NASA's Fermi Gamma-ray Space Telescope, support the idea that shock waves from the expanding debris of stars that exploded as supernovas accelerate cosmic rays up to energies of 1,000 trillion electron volts (PeV). That's 10 million times the energy of medical proton beams used to treat cancer. ISS-CREAM data will allow scientists to examine how sources other than supernova remnants contribute to the population of cosmic rays.

Protons are the most common cosmic ray particles, but electrons, helium nuclei and the nuclei of heavier elements make up a small percentage. All are direct samples of matter from interstellar space. But because the particles are electrically charged, they interact with galactic magnetic fields, causing them to wander in their journey to Earth. This scrambles their paths and makes it impossible to trace cosmic ray particles back to their sources.

"An additional challenge is that the flux of particles striking any detector decreases steadily with higher energies," said ISS-CREAM co-investigator Jason Link, a researcher at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "So to better explore higher energies, we either need a much bigger detector or much more observing time. Operating on the space station provides us with this extra time."

Large ground-based systems study cosmic rays at energies greater than 1 PeV by making Earth's atmosphere the detector. When a cosmic ray strikes the nucleus of a gas molecule in the atmosphere, both explode in a shower of subatomic shrapnel that triggers a wider cascade of particle collisions. Some of these secondary particles reach detectors on the ground, providing information scientists can use to infer the properties of the original cosmic ray.

These secondaries also produce an interfering background that limited the effectiveness of CREAM's balloon operations. Removing that background is another advantage of relocating to orbit.

With decreasing numbers of particles at increasing energies, the cosmic ray spectrum vaguely resembles the profile of a human leg. At PeV energies, this decline abruptly steepens, forming a detail scientists call the "knee." ISS-CREAM is the first space mission capable of measuring the low flux of cosmic rays at energies approaching the knee.

"The origin of the knee and other features remain longstanding mysteries," Seo said. "Many scenarios have been proposed to explain them, but we don't know which is correct."

Astronomers don't think supernova remnants are capable of powering cosmic rays beyond the PeV range, so the knee may be shaped in part by the drop-off of their cosmic rays in this region.

"High-energy cosmic rays carry a great deal of information about our interstellar neighborhood and our galaxy, but we haven't been able to read these messages very clearly," said co-investigator John Mitchell at Goddard. "ISS-CREAM represents one significant step in this direction."

ISS-CREAM detects cosmic ray particles when they slam into the matter making up its instruments. First, a silicon charge detector measures the electrical charge of incoming particles, then layers of carbon provide targets that encourage impacts, producing cascades of particles that stream into electrical and optical detectors below while a calorimeter determines their energy. Two scintillator-based detector systems provide the ability to discern between singly charged electrons and protons. All told, ISS-CREAM can distinguish electrons, protons and atomic nuclei as massive as iron as they crash through the instruments.

ISS-CREAM will join two other cosmic ray experiments already working on the space station. The Alpha Magnetic Spectrometer (AMS-02), led by an international collaboration sponsored by the U.S. Department of Energy, is mapping cosmic rays up to a trillion electron volts, and the Japan-led Calorimetric Electron Telescope (CALET), also located on the Kibo Exposed Facility, is dedicated to studying cosmic ray electrons.


Overall management of ISS-CREAM and integration for its space station application was provided by NASA’s Wallops Flight Facility on Virginia’s Eastern Shore. ISS-CREAM was developed as part of an international collaboration led by the University of Maryland at College Park, which includes teams from NASA Goddard, Penn State University in University Park, Pennsylvania, and Northern Kentucky University in Highland Heights, as well as collaborating institutions in the Republic of Korea, Mexico and France.

Quelle: NASA

 

 

Tags: Raumfahrt - ISS-ALLtag: New Mission Going to the Space Station to Explore Mysteries of 'Cosmic Rain' 

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Samstag, 12. August 2017 - 13:00 Uhr

Astronomie - August 2017 Brings Perseid Meteor Shower -Update

2.08.2017

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perseide-1

The 2017 Perseid meteor shower — which peaks Aug. 12 — will be sandwiched between a lunar eclipse and the much-heralded 2017 total solar eclipse, marking a month of excitement in the night (and daytime) sky.

The Perseid meteor shower is one of the most-watched showers of the year when it peaks each August; during that time, its rate can reach from 80 to 100 meteors per hour, and it's known for bright fireballs in the sky. This year, because of a bright, waning moon, visibility for observers will be closer to 40 or 50 meteors per hour — but it will still be a vivid show for viewers on the nights of Aug. 11 to 12 and Aug. 12 to 13.

"The Perseid peak is expected to occur at around 1 p.m. EDT on Aug. 12 this year, which is in the middle of the day," NASA asteroid expert Bill Cooke told Space.com in an email. "This means there will be good rates on either side. I think things may be slightly better in the pre-dawn hours of the 12th, but there should still be a decent show on either night."

Before settling in for the Perseids' peak, on the evening of Aug. 7 to 8, skywatchers will be treated to this month's full moon, known as the Full Sturgeon Moon. And for lucky skywatchers in Africa, Asia and Australia, a partial lunar eclipse will be visible as well, as Earth's shadow passes over the moon. 

That event happens when the moon has set over the United States, but don't worry; lunar and solar eclipses come in pairs, and the following total solar eclipse, on Aug. 21, is set to cross the continental United States coast to coast. Read our 2017 total solar eclipse guide to prepare for it and learn what the eclipse will look like in your area.

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Eclipses are reminders that the Earth and moon are constantly in motion; meteor showers further show that Earth is not moving around the sun in isolation. The Perseid meteor shower occurs every year as Earth passes through the trail of dust and debris left behind by Comet Swift-Tuttle, which orbits the sun in a much more oblong path than Earth's. The comet last passed by Earth in 1992 and will swing by again in 2126.

The meteor shower's intensity is determined by the thickness of the stream on a given year — last year, for instance, the meteor shower was in "outburst," and so there were a higher rate of meteors than usual. Researchers have only had the computer power to predict Perseid outbursts since the 1990s.

 

Even with the moon dampening the proceedings, the Perseids should still be an impressive show, according to Cooke.

"The good news is that the Perseids are rich in fireballs; otherwise, the moon would really mess with them," Cooke said. [Perseid Meteor Shower 2017: When, Where & How to See It]

Perseid Meteor Shower Quiz: Test Your Cosmic Fireworks Smarts
The Perseid meteor shower is one of the most spectacular meteor showers of the year, occurring in early August. How much do you know about the celestial light show? 

 

The Perseids appear to radiate from the constellation Perseus, and they are best seen from the Northern Hemisphere, although they can also be seen down into the midsouthern latitudes. They should be visible after about 10 p.m. local time Aug. 11, and they will increase in frequency all the way to dawn. Then, the next night, the Perseids rates will slowly decrease.

Remember, though they appear to radiate from one spot, the Perseids can appear all over the sky; to see them, lean back and look upward, and make sure you give yourself time to adjust to the dark. The naked eye is a better choice than a telescope or binoculars for viewing them, because the more of the sky you can see at once, the more likely it is you'll see the meteors and fireballs streak by. Ideally, Cooke said, you should devote a few hours at least to get the most out of the Perseids' peak — just don't fall asleep.

Quelle: SC

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Update: 6.08.2017

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Erste Meldung einer sehr hellen Perseide mit langer verblassenden Spur ("4 Häuser-Breite") über Alsenborn gegen 22.20 MESZ über unsere Meldestelle-Tel-Hotline.

CENAP-Meldestelle

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Update: 12.08.2017

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Weitere E-Mails und Tel-Anrufe über "große Sternschnuppe", "helle birnenförmige Leuchte", "Wow, so ein großen Komet habe ich noch nicht gesehen", nur eine kleine Auswahl an Beschreibungen der insgesamt 9 Melder aus dem norddeutschen Raum erreichten uns gegen Mitternacht von 11. auf 12.August.

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Perseiden 2017Sternschnuppen aus dem Labor

Mitte August kreuzt die Erde die Bahn des Kometen Swift-Tuttle. Dabei gelangen Kometenpartikel in die Erdatmosphäre – Sternschnuppen entstehen. Foto: dpa
Mitte August kreuzt die Erde die Bahn des Kometen Swift-Tuttle. Dabei gelangen Kometenpartikel in die Erdatmosphäre – Sternschnuppen entstehen. Foto: dpa

Stuttgarter Forscher züchten Sternschnuppen – sie wollen den Absturz von Meteoriten besser verstehen. Wie das funktionieren soll, hat unser Autor bei einem Besuch im Labor herausgefunden. 

 

Stuttgart - Mit einem Wunsch in der „Nacht der Wünsche“ wird es bei vielen Sternguckern wohl nicht klappen: Für die Nacht zum Sonntag, die ergiebigste Nacht des Perseidenschauers, macht der Deutsche Wetterdienst (DWD) wenig Hoffnung auf einen wolkenlosen Himmel. „Es gibt voraussichtlich einen breiten Streifen dichter Bewölkung über der Mitte Deutschlands“, sagte ein Sprecher. Am ehesten könne am Alpenrand und nördlich der Mittelgebirge auf vorübergehende Auflockerung gehofft werden.

 
 

Ein Blick zum Nachthimmel lohnt aber auch vorher – und nach dem Sonntag. Denn der Sternschnuppenregen, den der Komet Swift-Tuttle allsommerlich beschert, wenn die Erde seine Umlaufbahn kreuzt, hält ein paar Nächte an. Es ist ein ganzer Schweif an Staubkörnchen, den dieser eisige Himmelskörper hinter sich herzieht. Beim Eintritt in die Erdatmosphäre werden sie abgebremst und erhitzt; umliegende Gasteilchen werden angeregt, teilweise ionisiert und leuchten dadurch auf. 

Aus aller Welt lassen sich die Forscher Proben von echten Meteoriten schicken

Dem Sternenexperten Stefan Löhle sind die Wetterverhältnisse schnuppe. Auch braucht er keinen Perseidenschauer, um seiner Arbeit nachzugehen. Mit seinem Team von der Arbeitsgruppe HEFDiG (High Enthalpy Flow Diagnostics Group) produziert er seine eigenen Sternschnuppen im Labor. Aus aller Welt lassen sich die Wissenschaftler dafür Proben von echten Meteoriten schicken, die einst vom Himmel gefallen sind. Sie verglühen die Gesteinsproben in einem Plasmawindkanal, beobachtet und dokumentiert von verschiedensten Messgeräten. 

Von den Laborwerten versprechen sich die Forscher Erkenntnisse über die chemische Zusammensetzung und das genaue Verhalten beim Absturz von echten Sternschnuppen und Meteoroiden – und über deren mögliche Gefahren, etwa ab welcher Masse ein Meteoroid gefährlich ist. Im Plasmawindkanal simulieren die Wissenschaftler die Bedingungen, die ein Meteoroid beim Eintritt in die mittlere Erdatmosphäre in 80 Kilometer Höhe erfährt.

Der Murchison-Meteorit ist 1969 im Südosten Australiens gefallen

Die heutige Probe ist besonders, nicht nur der weiten Anreise wegen. Der Murchison-Meteorit ist 1969 im Südosten Australiens gefallen. Als kohlenstoffhaltiger Chondrit gehört er zu einer seltenen Klasse von Meteoroiden – seit Milliarden von Jahren reisen sie fast unverändert durch das Universum. Rund 100 Kilogramm an Material konnten Forscher insgesamt rund um den Ort Murchison bergen; einige Gramm des Steins hält Stefan Löhle nun in der Hand. Einen Zentimeter im Durchmesser, einen Zentimeter in der Länge misst der Stift; helle Sprenkel zieren das dunkle, matte Material.

Die Plasmawindkanäle des IRS bestehen aus sechs Meter langen, zwei Meter hohen, wassergekühlten Röhren. Sie wurden ursprünglich installiert, um den Hitzeschutz von Raumfahrzeugen zu testen – doch sie eignen sich auch, um den Absturz von Satellitenteilen, Weltraumschrott oder eben Meteoroiden zu simulieren. Im vorderen Drittel eines der Kanäle haben die Forscher ihre Probe auf eine bewegliche Halterung montiert. Langsam schließt sich der Deckel des Tanks, ein schriller Ton pfeift durchs Labor – eine Vakuumpumpe saugt die Luft aus dem Hohlraum. Die Ingenieure werfen einen letzten prüfenden Blick durch die Fotokamera oben auf dem Tank, kontrollieren die seitlich aufgebauten Lichtfeldkameras, checken die Highspeed-Videokamera und das Spektrometer. Dann wird die Zündung betätigt. Neun Ingenieure ziehen ihre dunklen Schutzbrillen auf und drängen sich gespannt vor viel zu kleinen Bullaugen. Im Tankdeckel sitzt der Plasmagenerator: Zwischen den beiden Elektroden des Generators liegt eine hohe Gleichspannung an, die sich in einem Lichtbogen entlädt. Nun wird von hinten ein Gasgemisch eingeblasen, schlagartig erhitzt und ionisiert – ein bläulich leuchtender, gut 11 000 Grad Celsius heißer Plasmastrahl schießt in den stählernen Kanal. Gleichzeitig setzt sich die Meteoritenprobe in Bewegung, fährt auf ihrer Halterung in den Plasmastrahl hinein.

Das Gestein verwandelt sich in eine rot wabernde Masse

Erst glüht sie an der Spitze, ein kleiner, orangerot leuchtender Fleck. Er flackert, wird größer, langsam überzieht er die ganze Probe, bis sich das Gestein in eine einzige rot wabernde Masse verwandelt hat; einzelne Tropfen lösen sich im Plasmastrahl, ziehen eine leuchtende Spur, verpuffen im heißen Nichts. Ein feuriges Spektakel, einer Sternschnuppe würdig – und wie diese auch nach vier Sekunden schon vorbei. Neun Ingenieure schieben ihre Schutzbrillen wieder zurück in die Stirn. „Ich glaube“, sagt Stefan Löhle, „das könnt ich mir hundert Jahre lang angucken.“

Zuerst allerdings geht es an die Auswertung der Daten. Die Helligkeit beispielsweise wird mit der Masse der Probe abgeglichen, die Lichtspektren mit der bekannten chemischen Zusammensetzung. Damit können die Messinstrumente kalibriert werden, die von der Erde aus die echten Sternschnuppen am Himmel analysieren – und Aussagen über deren Gewicht und Material treffen. Daraus wiederum lassen sich Rückschlüsse ziehen, aus welchem Teil des Sonnensystems ein Meteoroid stammt. Auch helfen die Messungen im Plasma, mehr über die Flugkurven und das Absturzverhalten von jenen dicken Brocken zu erfahren, die nicht komplett verglühen – und als Meteoriten auf die Erdoberfläche treffen. 

Meteoriden und Asteroiden sind auf möglichem Kollisionskurs 

Verschiedene Forschungsprogramme erarbeiten Strategien zur Abwehr von Meteoroiden und Asteroiden auf potenziellem Kollisionskurs. Die Sternschnuppen aus dem Labor helfen, diese Objekte besser verstehen und berechnen zu können.

Quelle: Struttgarter Nachrichten


Tags: Perseiden Meteor-Strom Astronomie - August 2017 Brings Perseid Meteor Shower 

908 Views

Samstag, 12. August 2017 - 07:30 Uhr

Raumfahrt - Roboter arbeiten bei Notwendigkeit für Weltraum-Ärzte

12.08.2017

Robots Are Cutting Down on the Need for Space Doctors

 Automated medical systems and remote controls mean fewer personnel per mission.
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Astronaut Michael Barratt works the controls at the Canadarm2 robotic workstation in the Destiny laboratory of the International Space Station.

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Man vs. Machine examines the ways in which technology promises to simplify our lives—or, for some of us, threatens to upend them.

NASA has largely computerized routine tasks such as orbital rendezvous, docking, and trajectory mapping; it’s also been developing “robonauts” since the late 1990s, including medical systems that can perform tests and procedures while controlled remotely by a doctor—or, in some cases, handle things without any human involvement.

 

The Benefit

Automation has made working and traveling in space less dangerous and reduced the number of personnel needed on a typical mission.

 

Innovator

  • Michael Barratt
  • Age: 58
  • NASA astronaut and flight surgeon
  • Location: Camas, Wash.

Background

Barratt helped write the book on how to handle medical problems in space. He also played a role in bringing NASA’s space medicine program to the Shuttle-Mir project and the International Space Station.

 

Close Call

In 2009, when Barratt was flying a mission to the ISS, his craft’s automated docking system failed, requiring manual override. “Any time you have a machine, you count on it breaking in spaceflight,” he says.

Tasks

NASA doctors are using telemedicine and remote controls to treat motion sickness and minor trauma in space. Barratt says he also monitors crew members’ levels of stress and other possible psychological issues. “We don’t use robot systems to judge human anxiety,” he says, alluding to the murderous HAL operating system from Stanley Kubrick’s 2001: A Space Odyssey.

Safeguards

Even though much of the drudgery of space travel has been automated, astronauts are trained to expect malfunctions. Humans still hand-check calculations for trajectory and motion-control guidance, Barratt says: “Both humans and computers have glitches.”

The Verdict

Is there a point at which machines can do all space medicine? Not likely. But if space colonies become a reality, more robots will be needed. “Our mission is the expansion of civilization outward,” Barratt says. “To be a multiplanet species, as a survival mechanism, we see a blend of human and machine supporting those efforts. You need both.”

Quelle: Bloomberg


Tags: Raumfahrt - Roboter arbeiten bei Notwendigkeit für Weltraum-Ärzte 

521 Views

Freitag, 11. August 2017 - 22:40 Uhr

Astronomie - NASA Webb Telescope bekommt seine Gestalt - Update-10

2.05.2017

James Webb Space Telescope will soon leave NASA Goddard for next phase of testing

 

The James Webb Telescope is ready to leave the NASA Goddard Space Flight Center— where the core of the observatory was constructed — and move on to the next phase in its journey to space.

NASA officials said Monday that Webb, the successor to the Hubble Space Telescope, has passed the last of its tests at the Greenbelt facility. 

It will soon be shipped to the NASA Johnson Space Center in Houston for its next round of testing.

"The Webb telescope is about to embark on its next step in reaching the stars as it has successfully completed its integration and testing at Goddard," Bill Ochs, NASA's Webb telescope project manager, said in a statement. "It is also a sad time as we say goodbye to the Webb Telescope at Goddard, but are excited to begin cryogenic testing at Johnson." 

The telescope has been in development, construction and assembly process for two decades, and its mirror and instruments have come together in a massive clean room at Goddard just over the past several years.

It is designed to see farther into space, and with greater sensitivity to light, than the Hubble. Its observations are expected to revolutionize understanding of the early universe, just as Hubble did starting in the 1990s, and to explore distant Earth-like planets in ways Hubble cannot.

The telescope's observatory, including its 21-foot mirror and set of four science instruments, spent months facing a battery of tests designed to show it can withstand the violent vibrations and loud sounds it will experience when it's launched next year.

Now, it will be tested in a large cryochamber at the Johnson center to prove it can operate in the chill of space.

NASA officials would not say when the move to Houston will occur, citing security concerns.

From there, the observatory is headed for Northrop Grumman Aerospace Systems in Redondo Beach, Calif., where it will be integrated with its six-layer sun shield that protects the instruments and mirror from interference.

It will travel by barge from California, through the Panama Canal, to French Guiana on the northern coast of South America, for its launch, slated for next October. The European Space Agency has a space port there.

Quelle: THE BALTIMORE SUN

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NASA’s Webb Telescope Completes Goddard Testing, Heading to Texas for More

NASA’s James Webb Space Telescope has successfully passed the center of curvature test, an important optical measurement of Webb’s fully assembled primary mirror prior to cryogenic testing, and the last test held at NASA's Goddard Space Flight Center in Greenbelt, Maryland, before the spacecraft is shipped to NASA’s Johnson Space Center in Houston for more testing.

James Webb Space Telescope
The James Webb Space Telescope completed its environmental testing at NASA's Goddard Space Flight Center in Greenbelt, Maryland. The Webb telescope will be shipped to NASA's Johnson Space Center in Houston for end-to-end optical testing in a vacuum at its extremely cold operating temperatures.
Credits: NASA/Chris Gunn

After undergoing rigorous environmental tests simulating the stresses of its rocket launch, the Webb telescope team at Goddard analyzed the results from this critical optical test and compared it to the pre-test measurements. The team concluded that the mirrors passed the test with the optical system unscathed.

 

“The Webb telescope is about to embark on its next step in reaching the stars as it has successfully completed its integration and testing at Goddard. It has taken a tremendous team of talented individuals to get to this point from all across NASA, our industry and international partners, and academia,” said Bill Ochs, NASA’s Webb telescope project manager. “It is also a sad time as we say goodbye to the Webb Telescope at Goddard, but are excited to begin cryogenic testing at Johnson.”

 

Rocket launches create high levels of vibration and noise that rattle spacecraft and telescopes. At Goddard, engineers tested the Webb telescope in vibration and acoustics test facilities that simulate the launch environment to ensure that functionality is not impaired by the rigorous ride on a rocket into space.

 

Before and after these environmental tests took place, optical engineers set up an interferometer, the main device used to measure the shape of the Webb telescope’s mirror. An interferometer gets its name from the process of recording and measuring the ripple patterns that result when different beams of light mix and their waves combine or “interfere.”

Waves of visible light are less than a thousandth of a millimeter long and optics on the Webb telescope need to be shaped and aligned even more accurately than that to work correctly. Making measurements of the mirror shape and position by lasers prevents physical contact and damage (scratches to the mirror). So, scientists use wavelengths of light to make tiny measurements. By measuring light reflected off the optics using an interferometer, they are able to measure extremely small changes in shape or position that may occur after exposing the mirror to a simulated launch or temperatures that simulate the subfreezing environment of space.

During a test conducted by a team from Goddard, Ball Aerospace of Boulder, Colorado, and the Space Telescope Science Institute in Baltimore, temperature and humidity conditions in the clean room were kept incredibly stable to minimize fluctuations in the sensitive optical measurements over time. Even so, tiny vibrations are ever-present in the clean room that cause jitter during measurements, so the interferometer is a “high-speed” one, taking 5,000 “frames” every second, which is a faster rate than the background vibrations themselves. This allows engineers to subtract out jitter and get good, clean results on any changes to the mirror's shape.

“Some people thought it would not be possible to measure beryllium mirrors of this size and complexity in a clean room to these levels but the team was incredibly ingenious in how they performed these measurements and the results give us great confidence we have a fantastic primary mirror,” said Lee Feinberg, Webb’s telescope optical element manager.

The Webb telescope will be shipped to Johnson for end-to-end optical testing in a vacuum at its extremely cold operating temperatures. Then it will continue on its journey to Northrop Grumman Aerospace Systems in Redondo Beach, California, for final assembly and testing prior to launch in 2018. 

Quelle: NASA

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Update: 8.05.2017

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James Webb Space Telescope Arrives at NASA’s Johnson Space Center

 

sttars
The James Webb Space Telescope is pushed into the clean room of Building 32. Building 32 houses Chamber A, the thermal vacuum chamber where the telescope will have its final thermal vacuum testing.
Credits: NASA/Chris Gunn

NASA's James Webb Space Telescope has arrived at NASA’s Johnson Space Center in Houston, Texas, where it will undergo its last cryogenic test before it is launched into space in 2018.

 

The telescope was loaded onto a trailer truck from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and moved slowly down a highway by the Webb team to Joint Base Andrews in Maryland. At Andrews, the entire tractor-trailer, with telescope inside, was driven into a U.S. Air Force C-5C aircraft and flown to Ellington Field in Houston, Texas.

 

When the C-5 landed at Ellington, the cargo was carefully unloaded and trucked to NASA Johnson, where inside a cleanroom the telescope was removed from its special shipping container. In the coming weeks it will be prepared for a key cryogenic test that will run nearly 100 days.

To ensure the telescope's optics will operate at its frigid destination 1 million miles out in space, it must complete tests at cryogenic temperatures in a vacuum. The biggest and final cryogenic-vacuum test occurs in Johnson's Chamber A, the same vacuum chamber where Apollo spacecraft were tested. This test is critical in that it will verify the performance of the whole telescope as a system end-to-end at its extremely cold operating temperatures. Subsequently, the telescope will continue on its journey to Northrop Grumman Aerospace Systems in Redondo Beach, California, for final assembly and testing with the spacecraft bus and sunshield prior to launch in 2018. 

The James Webb Space Telescope is the world’s most advanced space observatory. This engineering marvel is designed to unravel some of the greatest mysteries of the universe, from discovering the first stars and galaxies that formed after the big bang to studying the atmospheres of planets around other stars. It is a joint project of NASA, ESA (the European Space Agency) and the Canadian Space Agency.

Quelle: NASA

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Update: 10.05.2017

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Two James Webb instruments are best suited for exoplanet atmospheres

spectrum3

UNIVERSITY PARK, Pa. — The best way to study the atmospheres of distant worlds with the James Webb Space Telescope, scheduled to launch in late 2018 will combine two of its infrared instruments, according to a team of astronomers.

"We wanted to know which combination of observing modes (of Webb) gets you the maximum information content for the minimum cost," says Natasha Batalha, graduate student in astronomy and astrophysics and astrobiology, Penn State, and lead scientist on this project. "Information content is the total amount of information we can get from a planet's atmospheric spectrum, from temperature and composition of the gas — like water and carbon dioxide — to atmospheric pressures."

Batalha and Michael Line, assistant professor, School of Earth and Space Science, Arizona State University, developed a mathematical model to predict the quantity of information that different Webb instruments could extract about an exoplanet's atmosphere.

Their model predicts that using a combination of two infrared instruments — the Near Infrared Imager and Slitless Spectrograph (NIRISS) and the G395 mode on the Near Infrared Spectrograph (NIRSpec) — will provide the highest information content about an exoplanet's atmosphere.

NIRISS is a versatile camera and spectrograph that will observe infrared wavelengths similar to those the Hubble Telescope covers. NIRISS, according to Batalha and Line, should be combined with the G395 mode on NIRSpec, which will observe targets in longer infrared wavelengths at Webb's highest resolution.

Three main characteristics affect how much information an instrument can extract — resolution, maximum observable brightness, and wavelength range. These combined determine the total observable fraction of the information content of a planet's atmospheric spectrum.

Both NIRISS and NIRSpec will observe near-infrared wavelengths, the region of the electromagnetic spectrum in which the stars that exoplanets orbit around shine brightest. NIRISS is poised to measure a strong signature of water and NIRSpec can do the same for methane and carbon dioxide, three chemical compounds that provide a substantial amount of information about an atmosphere.

Batalha and Line tested each of ten likely observing methods on its own and in every possible combination with the other methods to determine which would maximize the total information content.

They retrieved the information from a set of simulated planets with temperatures and compositions that cover the range of previously observed exoplanet atmospheres. By comparing the retrievable information content in each planet's atmosphere, Batalha and Line found that this one combination of NIRISS and NIRSpec modes gives the most information regardless of the exoplanet's temperature or composition. The researchers published these results in The Astronomical Journal.

"We won't know a planet's temperature ahead of time," says Batalha. "If you're going to do a shot in the dark observation, you have the greatest chance of getting the information you want with this combination of instruments."

As an exoplanet crosses between its host star and Earth's telescopes, some of the star's light passes through the exoplanet's atmosphere. The exo-atmosphere leaves its fingerprint in the star's light — the planet's transmission spectrum — from which astronomers can learn about the exo-atmosphere's temperature, chemical composition and structure. The researchers' information content analysis focuses on the information retrievable from the transmission spectrum of a planet.

While Webb will not launch until late 2018, but astronomers are already planning the first set of observations they would like from the telescope.

"If we can strategize now," says Batalha, "by the time the first cycle of formal proposals comes around we can ensure that we are picking the best modes for larger proposals and not waste valuable observing time. This way everyone starts on an even playing field with the science."

While they highlight two NIRISS and NIRSpec modes as the best combination for observing most exo-atmospheres, Batalha and Line explain that the other modes will still be useful to observe different features of exo-atmospheres that the astronomers have not tested for, like clouds, haze and atmospheres hot enough to emit their own light.

"In the future," Batalha says, "there will be a push to characterize the first Earth 2.0. If we don't nail this down now and master the art of characterizing exo-atmospheres, we will never accurately characterize Earth 2.0."

The National Science Foundation, the Kavli Summer Program in Astrophysics, the NASA Astrobiology Program Early Career Collaboration Award, and the NASA Hubble Fellowship supported this research.

Quelle: University Park, Pennsylvania

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Update: 14.05.2017

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James Webb Space Telescope moving forward – latest milestone for Airbus contributions to the mission 

 

James Webb telescope and instrument module shipped by NASA from Goddard Space Flight Centre in Washington to Johnson Space Centre in Houston for final tests 

Houston 08/05/2017 – OTIS (Optical Telescope Element and Integrated Science), the payload module hosting the telescope and the instruments for the giant James Webb Space Telescope (JWST) has been shipped by NASA to the Johnson Space Centre (JSC) in Houston, Texas. OTIS includes two European instruments with major Airbus contributions, the near-infrared spectrograph NIRSpec built by Airbus and the mid-infrared instrument MIRI built with the support of Airbus.

NIRSpec, weighing 200kg, will be able to detect the faintest radiation from the most distant galaxies, observing more than 100 of them simultaneously. It will observe large samples of galaxies and stars at unprecedented depths across large swathes of the Universe and far back in time. Once launched, NIRSpec, known as the ‘super eye’, will operate at a temperature of -238°C. The instrument was developed by Airbus for the European Space Agency (ESA). 

 The MIRI instrument is a combined camera, spectrograph and coronagraph for mid-infrared wavelengths that will extend JWST’s observation capabilities to longer wavelengths, vital for the study of light from objects in the early universe or to peer inside dust clouds where stars and planetary systems are forming today. MIRI was developed by a European consortium of 21 institutes from 10 ESA member states as well as NASA’s Jet Propulsion Laboratory and Goddard Space Flight Centre, led by the UK’s Astronomy Technology Centre with project management from Airbus.

“This is a fantastic next step for the James Webb Space Telescope – bringing it one step closer to launch on Ariane 5,” said Nicolas Chamussy, Head of Space Systems. “JWST will enable us to study the early Universe and peer inside dust clouds to study star formation. This spacecraft represents the pinnacle of technology for modern astronomy, and shows Airbus’ outstanding expertise in support of the scientific research that JWST will carry out.”

 NASA, ESA, and the Canadian Space Agency (CSA) are collaborating to develop JWST, designed to be the next step after the legendary Hubble Space Telescope. After its launch in 2018 on an Ariane 5 launcher from Europe’s spaceport in Kourou, French Guiana, JWST will be the largest astronomical telescope in space. It will be able to study key phases in the evolution of the Universe in great detail – from the formation of the first stars and galaxies only a few hundred millions years after the Big Bang to the formation of planetary systems in our own Milky Way galaxy today.

Quelle: Airbus

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Update: 22.06.2017

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NASA's "Webb-cam" Captures Engineers at Work on Webb at Johnson Space Center

 

 

 

Webb in cleanroom at Johnson
NASA’s James Webb Space Telescope sits folded up in the cleanroom outside of Chamber A at NASA’s Johnson Space Center, Houston, Texas.
Credits: NASA/Desiree Stover
Webbcam image of JWST
This is an image taken from one of NASA’s two special "Webb-cams,” a camera in a giant clean room at NASA Goddard. The Webb-cams focus on what's happening with the very first completed instrument that will fly onboard the James Webb Space Telescope. The flight Integrated Science Instrument Module (ISIM) is at left center. The Ambient Optical Assembly Stand is on the right side of the image.
Credits: NASA

NASA's special "Webb-cam" kept an eye on the development of NASA's James Webb Space Telescope at NASA's Goddard Space Flight Center in Greenbelt, Maryland, since 2012. Now that Webb telescope has moved to NASA's Johnson Space Center in Houston, Texas, a special Webb camera was installed there to continue providing daily video feeds on the telescope's progress.

 

 

Space enthusiasts, who are fascinated to see how this next generation space telescope has come together and how it is being tested, are able to see the telescope’s progress as it happens by watching the Webb-cam feed online.

 

There were two Webb-cams at NASA Goddard. Those cameras, which were mounted inside the giant cleanroom, provided still photos (refreshed every minute) of the activity inside and gave a peek at what engineers and technicians were doing to the telescope as it came together. Over the last five years, Webb-cam viewers saw some amazing images of the Webb at Goddard, such as when all 18 gold-coated mirror segments of the Webb's primary mirror were mounted on the telescope.

 

"The two Webb-cams we installed in Goddard's giant cleanroom have developed a huge following over the last five years," said Maggie Masetti, social media manager and web developer on the Webb telescope mission at NASA Goddard. "With millions of views every month, you can bet that if there was a camera glitch, we heard about it right away."

 

The new "Webb-cam" is mounted where it has a view of the cleanroom at NASA Johnson Space Center. The camera fronts the chamber where the Webb telescope will be undergoing cryogenic testing in a massive chamber called "Chamber A." Although there is no view of Webb once it is inside the chamber during the actual cryo-optical testing, there will be much activity on Webb in the cleanroom itself for several weeks before and after

 

The Web camera at NASA’s Johnson Space Center can be seen online at: http://jwst.nasa.gov/, with larger views of the cams available at: http://jwst.nasa.gov/webcam.html.

The James Webb Space Telescope is the scientific successor to NASA's Hubble Space Telescope. It will be the most powerful space telescope ever built. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

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NASA's Webb Telescope Gets Freezing Summertime Lodging in Houston

NASA’s James Webb Space Telescope was placed in Johnson Space Center’s historic Chamber A on June 20, 2017, to prepare for its final three months of testing in a cryogenic vacuum that mimics temperatures in space.

NASA’s James Webb Space Telescope sits inside Chamber A at NASA’s Johnson Space Center, Houston.
NASA’s James Webb Space Telescope sits inside Chamber A at NASA’s Johnson Space Center, Houston.
Credits: NASA/Chris Gunn
NASA’s James Webb Space Telescope crossing the threshold into Chamber A at NASA’s Johnson Space Center, Houston on June 21, 2017
NASA’s James Webb Space Telescope crossing the threshold into Chamber A at NASA’s Johnson Space Center, Houston on June 21, 2017.
Credits: NASA/Chris Gunn

Engineers will perform the test to prove that the telescope can operate in space at these temperatures. Chamber A will simulate an environment where the telescope will experience extreme cold -- around 37 Kelvin (minus 236 degrees Celsius or minus 393 degrees Fahrenheit).

In space, the telescope must be kept extremely cold, in order to be able to detect the infrared light from very faint, distant objects. To protect the telescope from external sources of light and heat (like the sun, Earth, and moon), as well as from heat emitted by the observatory, a five-layer, tennis court-sized sunshield acts like a parasol that provides shade. The sunshield separates the observatory into a warm, sun-facing side (reaching temperatures close to 400 degrees Fahrenheit) and a cold side (185 degrees below zero). The sunshield blocks sunlight from interfering with the sensitive telescope instruments.

The James Webb Space Telescope is the scientific successor to NASA's Hubble Space Telescope. It will be the most powerful space telescope ever built. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

Quelle: NASA

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Update: 10.08.2017

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James Webb: Telescope's giant origami shield takes shape

SunshieldImage copyrightNORTHROP GRUMMAN CORP
Image captionThe shield's dimensions are 21.2m by 14.2m. Its five layers are made from a polyimide film known as kapton coated with aluminium

It is the size of a tennis court and next year it will go into orbit as part of the most sophisticated space telescope ever built. 

The kite-shaped object is a mask that will protect the James Webb observatory from the glare and heat of the Sun as it tries to image the deep Universe. 

Engineers have just finished joining together its individual layers. 

These membranes, made from a polymer material known as kapton, are as thin as a human hair. 

In their shade, the Webb telescope should be able to reach its operating temperature of less than 50 degrees above absolute zero (-223C). 

The finished shield is too big to fit in a rocket, however - as is the James Webb telescope.

Observatory and shield must therefore be folded up on themselves, origami style, for the ride to orbit. Only when they get into space can they be unpacked into an operational configuration. 

JWSTImage copyrightNASA/C.GUNN
Image captionWebb's primary mirror is made from segments that can be folded inwards

The Northrop Grumman Corporation in Redondo Beach, California, which leads the industrial consortium on the project, is currently packing and stowing the membranes ahead of deployment tests that will take place later this month. 

Assuming all goes to plan, the shield will then be attached to Webb's foldable mirrors and instruments. 

These elements are due arrive at Redondo Beach later in the year. 

They are presently in tests of their own at the US space agency's Johnson centre in Texas. These investigations aim to ensure the telescope can focus and analyse light properly. 

Mirror size comparison

James Webb is often described as the successor to the Hubble Space Telescope which is nearing the end of its mission life. 

The obvious difference is that Webb is much bigger. Its main mirror is 6.5m across versus Hubble's 2.3m. But the new observatory will also be working at longer wavelengths of light compared with its predecessor. 

Webb will sense in the near and mid-infrared range of the electromagnetic spectrum. This should allow the telescope to look deeper into space than Hubble, to see the very first stars to ignite in the cosmos more than 13 billion years ago. 

The James Webb Space Telescope is a joint endeavour of Nasa, and the European and Canadian space agencies. Its launch on a European Ariane rocket is currently scheduled for October 2018.

James Webb Space Telescope

Quelle: BBC

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NASA's Webb Telescope Summertime Deep-Freeze Continues

NASA's James Webb Space Telescope sits in Chamber A at NASA’s Johnson Space Center in Houston awaiting the door to close.
NASA's James Webb Space Telescope sits in Chamber A at NASA’s Johnson Space Center in Houston awaiting the colossal door to close.
Credits: NASA/Chris Gunn
Chamber A’s sealed, vault-like door towers over engineers at NASA’s Johnson Space Center in Houston.
Chamber A’s sealed, vault-like door towers over engineers at NASA’s Johnson Space Center in Houston.
Credits: NASA/Chris Gunn

NASA's James Webb Space Telescope began a nearly 100-day cryogenic test in a giant chamber in Texas in mid-July. Components of the Webb have previously endured similar tests to ensure they would function in the cold environment of space. Now all of those components are being tested together in the giant thermal vacuum known as Chamber Aat NASA's Johnson Space Center in Houston.

 

"A combination of liquid nitrogen and cold gaseous helium will be used to cool the telescope and science instruments to their operational temperature during high-vacuum operations," said Mark Voyton, manager of testing effort, who works at the NASA Goddard Space Flight Center in Greenbelt, Maryland. 

 

Next year, the tennis-court sized sunshield and spacecraft bus will be added to make up the entire observatory.

 

Previous Testing

 

In early 2016, the science instruments completed a series of similar cryogenic testing at NASA Goddard. For months, the components were tested inside the Space Environment Simulator.

 

Then, a "practice model" known as the “Pathfinder” telescope endured similar testing in Chamber A. The test confirmed that the real or flight Webb telescope could be done. NASA often rehearses with practice models to ensure all complicated test equipment works and that the precision-test conditions are achievable before subjecting an actual flight article to testing.

 

In early March 2017 at NASA Goddard,  Webb’s mirrors and instruments successfully concluded vibration and acoustic environmental testing. Those tests ensured Webb can withstand the vibration and noise created during the telescope's launch into space. Currently, engineers are analyzing this data to prepare for a final round of vibration and acoustic testing, once Webb is joined with the spacecraft bus and sunshield next year.

 

In May 2017, Webb journeyed to NASA Johnson, taking Pathfinder’s place inside the historic vacuum chamber, Chamber A.  

 

How and What Chamber A Will Do?

Vacuum pumps remove nearly 100% of the air from the chamber. Temperatures are cooled in Chamber A by coursing liquid nitrogen and cold gaseous helium through plumbing on the shrouds, which act as heat exchangers. That process drops the temperatures in the chamber to simulate conditions in space where the Webb telescope will orbit. "Of course the chamber stays under vacuum and the cryogens are flowed through the shroud plumbing to radiatively cool everything inside the chamber," said Paul Geithner, Webb’s deputy project manager - technical of NASA Goddard.

 

The testing is critical because these instruments must operate at around minus 387 Fahrenheit (minus 232.8 degrees Celsius or 40 Kelvin). This is 260 Fahrenheit (126.7 degrees Celsius) colder than any temperature ever recorded on Earth’s surface.

 

In Chamber A, the telescope will be cooled down so temperatures are steady and change very little with time, and then warmed up to room temperature or “ambient” conditions.  

SIDEBAR FEATURE:  How Does NASA’s Webb Telescope Stay Cool in Chamber A?

 

Monitoring the Testing

 

During the testing period, scientists and engineers will monitor the telescope with temperature sensors and cameras in Chamber A.

 

"As far as monitoring goes, there are many thermal sensors that monitor temperatures of the telescope and the support equipment," said Gary Matthews, an engineer on the Webb telescope at Goddard. "We also have some specialized camera systems that allow us to know the physical position of the hardware inside the chamber. That allows us to monitor how the Webb moves as it gets colder. Finally, there is a whole host of optical equipment that we will use to understand the performance of the telescope."

Download this video in HD formats from NASA Goddard's Scientific Visualization Studio http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=12186
Credits: NASA's Goddard Space Flight Center/M. McClare

What's Next After Chamber A?

 

Once the end-to-end cryo-optical testing is complete at NASA Johnson this fall, the telescope will journey to Northrop Grumman in Redondo Beach, California, where it will be integrated with the spacecraft and sunshield, thus forming the James Webb Space Telescope observatory. Once there, it will undergo more tests called "observatory-level testing." This testing is the last exposure to a simulated launch environment before flight and deployment testing on the whole observatory.

The James Webb Space Telescope is the world’s most advanced space observatory. This engineering marvel is designed to unravel some of the greatest mysteries of the universe, from discovering the first stars and galaxies that formed after the big bang to studying the atmospheres of planets around other stars. It is a joint project of NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA).

Quelle: NASA

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Update: 11.08.2017

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Webb Telescope's Critical Protective Sunshield Now Fully Installed

jwst-sunshield-northrop-grumma

A piece of hardware critical to the success of the James Webb Space Telescope (JWST) by preventing background heat from the Sun, Earth and Moon from interfering with the telescope’s sensitive infrared instruments is now fully installed, completed at Northrop Grumman Aerospace Systems in Redondo Beach, California earlier this week.

Quelle: AS

 

 

 


Tags: Webb Telescope NASA Webb Telescope bekommt seine Gestalt - Update-10 Astronomie - NASA Webb Telescope bekommt seine Gestalt - Update-10 NASA Webb Telescope 

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