"But" says Karl Battams of the Naval Research Lab, "prepare to be surprised. A new comet from the Oort Cloud is always an unknown quantity equally capable of spectacular displays or dismal failures."

The Oort cloud is named after the 20th-century Dutch astronomer Jan Oort, who argued that such a cloud must exist to account for all the “fresh” comets that fall through the inner solar system.  Unaltered by warmth and sunlight, the distant comets of the Oort cloud are like time capsules, harboring frozen gases and primitive, dusty material drawn from the original solar nebula 4.5 billion years ago.  When these comets occasionally fall toward the sun, they bring their virgin ices with them.

Because this is Comet Pan-STARRS first visit, it has never been tested by the fierce heat and gravitational pull of the sun.  "Almost anything could happen," says Battams.  On one hand, the comet could fall apart--a fizzling disappointment.  On the other hand, fresh veins of frozen material could open up to spew garish jets of gas and dust into the night sky.

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Update: 19.02.2013

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Comet Pan-STARRS (C/2011 L4), widely expected to become a naked-eye object in early March, is now closer to the sun than Venus. Solar heating is vaporizing the comet's icy core and creating a wide, fan-shaped tail visible through binoculars in the southern hemisphere. Ignacio Diaz Bobillo sends this picture from Buenos Aires, Argentina

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From about March 7, it will appear above the horizon in Hawaii. To see it, you will need an unobstructed, cloudless view of the western horizon. It is best to pick a dark spot, away from streetlights.

Look in the direction of the sunset just after the sun has gone down. The comet will be just above the horizon. The chart below shows the position of the comet in the western sky at 7:00 p.m. throughout the month of March.

The twilight sky will make the comet much harder to see than if it were high up in a dark sky, and moonlight will interfere with viewing the comet after March 13.

To see the comet’s tails, you may need a pair of binoculars.

Although the brightness of comets is notoriously difficult to predict ahead of time, scientists expect this comet will have a brightness similar to that of the stars in the bowl of the Big Dipper or Orion’s belt (magnitude 2 to 3).

March 13 may be the best time to take an interesting picture of the comet because on that evening, it will appear just below the thin crescent moon.

By the end of March, the comet will no longer be visible in the evening sky, but if you get up early, you may be able to see it in the eastern sky just before sunrise. However, by then the comet will be farther from both the sun and Earth, and will therefore be fainter.

Comets are balls of ice and dust. As they approach the sun, they heat up, and the ice begins to sublime—to change from ice into a gas. When that happens, they develop a coma, a large envelope of gas and dust that surrounds the solid nucleus, and two tails, a dust tail and an ion tail that consists of gas molecules ionized by sunlight. Each of these tails may be over a million miles long. It is because of the coma and tails that they become visible to the naked eye, sometimes spectacularly so.

Some comets, including Comet PANSTARRS, follow an orbit that begins in the very outer reaches of the solar system. As they pass by the planets, they receive a gravitational “kick” that propels them out of the solar system. Their sole visits to the inner solar system are therefore our only chance to see them.

Others, like Halley’s comet, have elliptical orbits, and return to the inner solar system again and again, although their orbits are sometimes so large that it takes hundreds or thousands of years for them to return.

The Pan-STARRS Project is being led by the University of Hawaii Institute for Astronomy, and exploits the unique combination of superb observing sites and technical and scientific expertise available in Hawaii. Funding for the development of the observing system has been provided by the United States Air Force Research Laboratory. The PS1 Surveys have been made possible through contributions by the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, the Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network, Incorporated, the National Central University of Taiwan, and the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate. Any opinions, findings, and conclusions or recommendations expressed in this article are those of the author(s), and do not necessarily reflect the views of the National Aeronautics and Space Administration.

Quelle:Institute for Astronomy at the University of Hawaii at Manoa

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"Both comets were faint but visible to the naked eye, C/2011 L4 (PanSTARRS) slightly brighter than C/2012 F6 (Lemmon)," says Cherney. "I would guestimate the visual magnitude of Comet Lemmon at +5.5 and PanSTARRS at +5." Also visible in Cherney's images are the Small Magellanic Cloud and the 47 Tuc globular star cluster.

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Our long-anticipated highlight for March is likely to be the emergence of Comet PANSTARRS in our evening twilight. Officially called Comet 2011 L4 (PANSTARRS) it reaches perihelion, its closest to the Sun (45 million km), on the 10th.

Our first sight of it may come two days later when it stands only 6° high in the W and the same distance to the left of the one-day-old Moon forty minutes after sunset. We will probably need binoculars, and certainly a clear horizon, to glimpse either object in the bright twilight. A day later the comet is 7° high and 7° below-right of the Moon. Updated predictions have it near the third magnitude at that time, with a dust tail stretching several degrees away to its upper-left.

The following days see it climb to pass 6° to the left of Algenib, the lower-left star of the Square of Pegasus, on the 16th and 7° left of Alpheratz, top-left in the Square, on the 23rd. By then it may be fainter than the fourth mag and its dust tail may be close to vertical. Expect more details here in Starwatch on the 11th.

With Mercury, Venus and Mars hidden in the Sun's glare from our latitudes this month, Jupiter, conspicuous high in our S sky at nightfall, is one of only two naked-eye planets on show. The other is Saturn which rises in the ESE minutes after our map times and passes some 24° high in the S five hours later. Saturn brightens from mag 0.4 to 0.3 in March, shows an 18 arcsec disc with rings 41 arcsec wide at mid-month and is passed by the Moon on the 2nd and 29th.

Jupiter dims from mag -2.3 to -2.1 as it slides eastwards above Aldebaran and the Hyades cluster in Taurus. The planet's cloud-banded disc appears 37 arcsec wide when the planet lies near the Moon on the 17th.

March diary

2nd 15h Moon 3˚ S of Saturn

4th 13h Mercury in inferior conjunction; 22h Last quarter

10th 04h Comet PANSTARRS at perihelion

11th 20h New moon

18th 01h Moon 1.5˚ S of Jupiter

19th 17h First quarter

20th 11:02 Vernal equinox

24th 18h Jupiter 5˚N of Aldebaran

27th 09h Full moon

28th 17h Venus in superior conjunction

29th 01h Uranus in conjunction with Sun; 20h Moon 3˚ S of Saturn

31st 01h GMT = 02h BST start of British Summer Time

The Guardian

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Update: 28.02.2013

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Comet C/2011 L4 PANSTARRS as seen from Mount Dale, Western Australia. The lights on the distant horizon are from the city of Armadale, which is southeast of Perth. Image credit: Astronomy Education Services/Gingin Observatory

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Update: 12.03.2013

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