The Eta Aquarid meteor shower is the legacy of Halley’s Comet in May’s night sky
Do you remember Halley’s Comet? The last time this famous object was visible was in 1986, 36 years ago.
You younger readers might have little or no memory of this famous cosmic vagabond (It takes roughly 75 years to go once around the sun; your next chance will come in the summer of 2061). Or maybe, if you were around back then, you didn’t see Halley’s Comet at all because of light pollution or the comet’s low altitude above the horizon.
Either way, if you missed out on the 1986 event, or don’t want to wait until the comet’s next flyby in 2061, you might want to step outside before sunrise during these next few mornings and try to catch a view of some “cosmic litter,” a meteor shower made up of debris that has been left behind in space by Halley’s Comet.
An image of Halley’s Comet taken in 1986. (Image credit: NASA)
The birth of a meteor shower
Meteoroids are the remnants of the wholly or partially broken apart nucleus, or solid core, of comets. Swarms of tiny particles — generally no larger than pebbles and sand grains — either come from comets or were formed with them. These particles generally remain near and along the comet’s orbit.
This material is originally “bunched up,” but eventually spreads out along the parent comet’s orbital path. If the swarm of particles is old enough, the cometary debris is distributed more or less uniformly all along the orbit of the parent comet. In other words, the meteoroids are distributed fairly evenly along their orbit around the sun. Because of this, the Earth, when it cuts across the orbit of the parent comet (or passes very near it), will receive a meteor shower of greater or less intensity at about the same time each year.
As it turns out, the orbit of Halley’s Comet closely approaches the Earth’s orbit at two different places. One point is in the middle to latter part of October, on the inbound leg of this comet’s approach to the sun, producing a meteor display known as the Orionids. The other point comes in the early part of May, on the comet’s outbound leg, producing what are called the Eta Aquarid meteor shower.
If you’re hoping to capture photos of Eta Aquarids, our guide on how to photograph meteor showers can help. Check out our best cameras for astrophotography and best lenses for astrophotography guides to prepare for the next meteor shower.
When and where to watch
According to Margaret Campbell-Brown and Peter Brown in the Royal Astronomical Society of Canada’s 2022 “Observer’s Handbook,” the Eta Aquarid meteor shower is predicted to peak early on Friday morning (May 6). Under ideal conditions (a dark, moonless sky) about 40 to 60 of these very swift meteors can be seen per hour — one of the best of the principal annual meteor displays. The very brightest of these meteors leave glowing, long-lasting trails behind them. And with a waxing crescent moon having set before 1 a.m. local daylight time, this is one of those years when observing conditions will be perfect. This shower appears at about one-quarter peak strength for about two or three days before and after May 6.
There is, however, a drawback if you plan to watch for these meteors this year — at least for those watching from north of the equator. The radiant (the emanation point of these meteors) is located near the asterism popularly known as “Water Jar” of the constellation Aquarius the Water Bearer, which comes above the eastern horizon around 2:30 a.m. local daylight time.
Now from the Southern Hemisphere, the Eta Aquarids is considered to be the best meteor display of the year. For places including Melbourne, Australia, Dunedin, New Zealand, Santiago, Chile and Cape Town, South Africa, the Water Jar of Aquarius climbs more than halfway up the eastern sky by the first light of dawn, allowing meteor observers to enjoy a very fine meteor show for a few hours.
However, it’s a much different story for those meteor observers living north of the equator, as the Water Jar of Aquarius never gets very high in the sky as seen from northern latitudes. And shortly after it first appears, the first light of dawn begins to brighten the eastern sky. Altogether, these factors make it very tough for those living in the northern hemisphere to see the meteor shower.
Because of this, the actual observed rates are usually much lower than the oft-quoted 40 to 60 per hour.
From the United States, typical rates are:
30 meteors per hour at 21 degrees north latitude (Honolulu, Hawaii),
25 meteors per hour at 26-degrees north latitude (Brownsville, Texas; Naples, Florida),
15 per hour at 35-degrees latitude (Albuquerque, New Mexico; Chattanooga, Tennessee),
Only 10 per hour at 40-degrees (Philadelphia, Pennsylvania; Salt Lake City, Utah).
About 5 or less north of latitude 45 (Bangor, Maine; Seattle, Washington).
Catch an Earthgrazer
For most skywatchers, one of the best outcomes from watching a meteor shower is to catch a glimpse of a meteor emerging from the radiant that will skim the atmosphere horizontally — much like a bug skimming the side window of an automobile. Meteor watchers call such shooting stars “Earthgrazers.”
These “Earthgrazers” leave colorful, long-lasting trails. “These meteors are extremely long,” says Robert Lunsford, of the American Meteor Society. “They tend to hug the horizon rather than shooting overhead where most cameras are aimed.” “Earthgrazers are rarely numerous,” cautions Bill Cooke, a member of NASA’s Space Environments team at the Marshall Space Flight Center. “But even if you only see a few, you’re likely to remember them.”
If you do catch sight of one early these next few mornings, keep in mind that you’ll likely be seeing the incandescent streak produced by material which originated from the nucleus of Halley’s Comet. When these tiny bits of comet collide with Earth, friction with our atmosphere raises them to white heat and produces the effect popularly referred to as “shooting stars.”
Put another way: Like all comets, Halley’s is a cosmic litterbug and, as such, it leaves behind in its wake a trail of — for lack of a better term — garbage, composed of tiny bits and crumbs of space debris that can produce beautiful incandescent trails upon impacting our atmosphere.
In a way, I guess you can call them “rock stars,” but eventually, they fall down to Earth.
Editor’s note: If you snap an amazing photo of an Eta Aquarid meteor or any other night-sky sight and you’d like to share it with Space.com for a story or image gallery, send images, comments and location information to [email protected].
Joe Rao serves as an instructor and guest lecturer at New York’s Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers’ Almanac and other publications. Follow us on Twitter @Spacedotcom and on Facebook.