29.12.2019

A Geminid meteor flashes across the sky on December 13, 2018.
Bob King

Of all the celestial sights visible during the year, meteor showers seem to captivate public interest more than most — and it's easy to understand why. For one thing, it's exciting to watch bits of space rock create sudden, white-hot streaks of light as they slam into Earth's atmosphere. Also, meteor showers are fairly predictable, coming at roughly the same times each year.

What are Meteors?

Also known as "shooting stars," meteors are bits of interplanetary debris that strike Earth's upper atmosphere at speeds of 30 to 70 km (20 to 45 miles) per second! And although some meteors look bright enough that it seems you can almost touch them, actually they occur very high up, at altitudes of 80 to 120 km (50 to 75 miles).

Derived from the Greek word meteoros (meaning "high in the air"), they're actually fairly common. If you look up into a dark, Moonless night sky from a location far from city lights, you'll see brief streaks from sporadic (random) meteors a few times every hour. They can occur at any time on any night and appear in any part of the sky.

Meteors can range in brightness from tiny blips just at the limit of visibility to dramatically bright fireballs that outshine Venus and light up the nightscape around you. The rarest of these, called a bolide, shatters explosively into pieces during its rapid descent and can even create a loud boom.

The little nuggets in Grape-Nuts cereal are a close match to the size of particles that typically create meteors in our atmosphere.
J. Kelly Beatty

Because they're arriving so fast, it doesn't take a very large particle to make a dramatic flash. Typically they're no bigger than big sand grains, and something the size of a pea can create a meteor that's dramatically bright. Those high velocities give each particle a lot of kinetic energy, which converts to heat due to friction in the upper atmosphere.

Many people think a meteor occurs because the particle is "burning up." But actually friction flash-heats air molecules along the particle's path to thousands of degrees. The air molecules cool down in just a split second, giving off light as they do so.

What is a Meteor Shower?

The Perseid meteor shower is so named because even though its "shooting stars" can appear anywhere in the sky, they can all be traced back to the constellation Perseus.
Sky & Telescope

Whenever Earth encounters a stream of gritty debris left in space by a passing comet, the result is a meteor shower.

You'll notice the difference if you watch the sky for a half hour or so during one of these events: Not only do the number of meteors you'll see go up, but also the meteors seem to fly away from a common point in the sky called the radiant.

This is a trick of perspective, because all these particles are traveling in parallel — part of a vast but sparse "river of rubble" that's spread all around the comet's orbit. To get a better sense of this, check out the interactive animation below, which is part of a set created by Ian Webster. It shows particles along the orbit of Comet 109P/Swift-Tuttle, which is the comet responsible for the Perseid meteor shower. (Have some fun with it: Click and drag to get different perspectives):

A shower gets its name not from its parent object but from the constellation where this radiant lies — for example, August's well-known Perseid shower has its radiant in Perseus, December's Geminids appear to radiate from Gemini, and so forth.

One notable exception to this rule is the Quadrantid shower, named for the now-defunct constellation Quadrans Muralis. Its radiant lies in the constellation Boötes. In any case, the higher a shower’s radiant, the more meteors it produces all over the sky.

Meteor showers are usually at their best after midnight, during the hours before dawn. The graphic below explains why: That's when you're on the side of Earth facing forward along its orbit. Earth circles the Sun at about 30 km (20 miles) per second, so any bits of interplanetary debris slam into the predawn sky even faster, making each meteor brighter than it would have been if it had hit earlier in the evening, when they catch up to Earth's trailing hemisphere.

In most cases, a meteor shower will appear its strongest in the hours before dawn (as at left) — when Earth's orbital velocity combines with the particles' velocity to increase arrival speeds. These same particles, hitting Earth's "trailing" side after sunset (right), will strike at relatively slower speed.
Sky & Telescope

Dynamicists have gotten rather good at predicting when a particular shower might display an extra burst of activity. Usually these are from concentrated "ribbons" of particles that might have been ejected by the parent comet decades or even centuries ago. For that reason, this year's list includes the Draconids on the night of October 6–7 (see the Draconids description below).

NASA scientists find that the Perseids produced more fireballs than any other annual meteor shower.
NASA-MSFC

Also, some meteor showers deliver a relatively high proportion of large particles, which can create impressive displays of fireballs. As the graph here shows, the Perseid, Geminid, and Orionid meteor showers create the most fireballs. "The average peak magnitude for a Perseid observed by our cameras is –2.7; for the Geminids, it is –2," explains NASA scientist Bill Cooke. "So on average, Geminid fireballs are about a magnitude fainter than those in the Perseids."

The descriptions and table below highlight the year's best and most dependable displays, but the International Astronomical Union now recognizes more than 100 well-defined meteor showers and hundreds of other candidates that haven't been confirmed. Most of these are so weak that it takes a trained observer to spot them.

Must-See Meteor Showers in 2020

Here are highlights of the major meteor showers for 2020. For the best possible viewing experience, find a dark location free from light pollution, make yourself comfortable in a reclining chair, and wear plenty of warm clothing (as appropriate). And for more information on watching and studying meteors, see our article on meteor basics and the other articles in the Meteor section of our website.

The dates listed below correspond to the predawn hours closest to the predicted peak, though a shower is often active a few nights before and after the peak date. The rates listed are for ideal conditions: very dark skies free of moonlight or light pollution, with the radiant nearly overhead. Most likely you'll see somewhat lower rates than those listed. Following the table are specific predictions for each shower's prospects during 2020.

January 4: The Quadrantids

Here's the view looking northeast at about 1 a.m., by which time the Quadrantid shower's radiant is well above the horizon for mid-northern viewers.
Sky & Telescope diagram

The "Quads" can deliver at least 1 meteor per minute under excellent sky conditions. In fact, the idealized zenithal hourly rate (ZHR), for someone with perfectly dark skies and the meteor's radiant overhead, is a very high 120 — in some years it's been 200!

But in practice few observers ever see anything close to this many, because the shower's maximum activity lasts only several hours and is easy to miss. Seeing 25 per hour is more typical. Fortunately, this year the peak occurs near 9^h Universal Time on January 4th — well timed for North America. The first-quarter Moon will set shortly after midnight, and after that the rate of activity should steadily increase until dawn. So bundle up, and go view the Quads!

The parent of this shower is an object designated 2003 EH₁, which loops around the Sun every 5½ years between the orbits of Earth and Jupiter. It's not an active comet — more likely it's an "extinct comet" that no longer has any ice. Meteor specialist Peter Jenniskens first realized that this body is responsible for the Quadrantid meteors.

April 22: The Lyrids

As with the Quadrantids, April's Lyrid shower puts on a fairly brief performance. This hasn't been a particularly strong display in recent years, though counts exceeded one per minute during an outburst in 1982. The predicted peak (near 6^h UT) is very favorable for North America, and the Moon is new, so (unlike last year) its light will not wash out the show this year. Any Lyrids you see will emanate from a radiant near the Hercules-Lyra border.

May 5: The Eta Aquariids

This annual shower originates from none other than Halley's Comet, and these meteors come in fast — 66 km (41 miles) per second! However, the shower's radiant (in the Water Jar asterism of Aquarius) never gets very high above the horizon for observers in the Northern Hemisphere. Also, it rises only a couple of hours before dawn. Worse yet, this year's peak will be spoiled by a nearly full Moon that remains in the sky virtually all night.

July 29: The Delta Aquariids

This long-lasting shower, more formally called the Southern Delta Aquariids, has a radiant below the celestial equator and thus, like the Eta Aquariids, is best seen from the Southern Hemisphere. However, northerners can view its radiant well above the southern horizon for a few hours before and after midnight. The SDA shower has a reputation for delivering a steady stream of meteors over several days, with counts as high as 20 per hour visible from the darkest locations.This year, the peak is actually on the evening of July 28th for North America, but your best views will come after midnight on the 29th, after the waxing gibbous Moon has set.

August 12: The Perseids

Even casual skywatchers know about the Perseid meteor shower, because it can deliver at least one meteor per minute under pleasant summer skies. But the shower's peak performance is relatively brief, so timing is important.

A bright Perseid meteor streaked down on August 7, 2010, over buildings at the Stellafane amateur astronomy convention in Springfield, Vermont.
Dennis di Cicco

For North Americans, the shower's maximum should come on the morning of August 12th. At that time the Moon will be slightly past third quarter, so it will rise around 11 p.m. and create an annoyance in the predawn hours when the shower is it's best. Meteor expert Peter Jenniskens predicts that an extra pulse of Perseids might appear near 10^h UT on the 12th, timing that favors the West Coast before dawn.

But this shower can be enjoyed on the evening of the 11th, as soon as its radiant (near the Double Cluster in Perseus) clears the northeastern horizon, by roughly 8 p.m. This is also when you'll most likely see bright fireballs that skim Earth's atmosphere and create long, dramatic streaks in the sky. And on that evening the Moon won't rise until about 11 p.m.

These meteors are bits of debris shed by Comet 109P/Swift-Tuttle, which orbits the Sun every 130 years. Careful observers first realized that the Perseids are an annual event in the 1830s.

October 7: The Draconids

This normally weak shower, which emanates from near the head of Draco, usually offers no more than about 10 faint meteors per hour at its peak, so it's not usually included in this annual roundup. However, astounding "storms" of Draconids occurred in 1933 and 1946 —  as recently as 2018 observers logged rates of up to 150 per hour. And 2020 might be another exceptional year for the Draconids. Two meteor specialists have independently predicted an outburst created by dense streams of particles ejected by this shower's parent comet, 21P/Giacobini-Zinner, in the years 1704 and 1711 — more than three centuries ago!

Earth should slide through these streams between 1:30 and 2:00 UT on October 7th. That's great timing for North America on the evening of the 6th, corresponding to 6:30 to 7:00 p.m. Pacific Daylight Time (9:30 to 10:00 p.m. EDT). A waxing gibbous Moon will be a problem after it rises around 9 p.m., so the best viewing might be right after dusk. Draconids are especially slow-moving, striking our atmosphere at  just 21 km (14 miles) per second.

October 21: The Orionids

Here's another modest shower due to Halley's Comet. This year its peak, early on October 21st, is well suited for observers in North America and Europe. Moonlight won't be a problem, and you can start watching around 9 p.m. on the 20th, after the shower's radiant (located above Orion’s bright reddish star Betelgeuse) clears the horizon. But the best rates, perhaps one meteor every few minutes, will come after midnight.

November 5: The Southern Taurids

Lasting from mid-September to mid-November, this broad, weak display typically produces at most a dozen meteors per hour at its peak. But defining that peak can be tricky: The International Meteor Organization predicts October 10th, while Canadian meteor researchers Margaret Campbell-Brown and Peter Brown state it'll be November 5th. Part of the confusion arises because the nearby but distinct Northern Taurid shower also peaks in early November. (The northern component comprises bits of debris shed by Comet 2P/Encke, whereas the southern one is from "asteroid" 2004 TG₁₀, which itself might be a fragment of Encke.)

In any case, let's go with November 5th, though you might want to wait a couple more days to sidestep the bright light from a waning, nearly full Moon. By then the radiants of these paired showers will both be in western Taurus, along its border with Cetus. You might notice that Taurid meteors don't zip across the sky very quickly — they strike the atmosphere at a relatively slow 19 miles (30 km) per second.

November 17: The Leonids

The Leonid shower's parent comet, 55P/Tempel-Tuttle, tends to create narrow concentrated streams of debris that produced prodigious displays in the late 1990s, when it last swung close to the Sun. Since then the shower's activity has varied from year to year, usually offering little more than a trickle of shooting stars radiating from Leo’s Sickle. This year's peak comes early on November 17th, so venture outside after midnight. Moonlight will not be an issue.

December 14: The Geminids

The Geminid meteors can flash into view anywhere in the late-night sky. But if you follow their paths back far enough, they all appear to diverge from a point in the constellation Gemini.
Sky & Telescope diagram

This end-of-the-calendar shower is usually the year’s best and most reliable, with upward of 100 meteors per hour radiating from a spot near the bright star Castor. The Geminid radiant is well up in the sky by 9 p.m. as seen from at mid-northern latitudes. Unlike last year's display, which was ruined by a just-past-full Moon, the 2020 Geminids arrive when the Moon is new.

Timing will be important, because this shower's peak is strong but brief (near 1 UT on the 14th). Once again, this is great timing for North Americans, especially in the eastern half (8 p.m. EST), on the evening of the 13th. This is a show you won't want to miss.

Geminid meteors come from 3200 Phaethon, an asteroid discovered in 1983 that circles the Sun every 3.3 years. In fact, recent observations suggest that Phaethon might be a "rock comet" that sheds particles when its surface heats up to roughly 1,300°F (700°C) at each perihelion.

December 22: The Ursids

Although the Ursid shower delivers only a modest 10 meteors per hour under even the best conditions, it has the advantage of having a radiant near the bowl of the Little Dipper — so it's in view all night from northern latitudes. Peak activity, which lasts just a few hours, is predicted for around 9^h UT — well timed for North America and Europe. You can start looking after it gets dark on the 21st, but you'll see more Ursids once the first-quarter Moon sets after midnight of the 22nd.

Quelle: Sky&Telescope