Early Thursday morning (May 6), just before dawn begins to light up the eastern sky, we'll have an opportunity to see some of the remnants of the most famous of comets briefly light up the early morning sky.
Halley's Comet made its last pass through the inner solar system in 1986 and is not due back until the summer of 2061. Nonetheless, each time Halley sweeps around the sun, it leaves behind a dusty trail — call it "cosmic litter" — that ends up trailing behind the comet.
And as it turns out, the orbit of Halley's Comet closely approaches the Earth's orbit at two places. One point is in the middle to latter part of October, producing a meteor display known as the Orionids. The other point comes in the early part of May, producing the Eta Aquarids.
When and where to watch
Under ideal conditions (a dark, moonless sky) about 30 to 60 of these very swift meteors might be seen per hour at the peak of the display on May 6. The shower appears at about one-quarter peak strength for several days before and after May 6. This year will be a very good year to watch for them because the moon will be in a waning crescent phase, just 28% illuminated and providing little interference for viewing these swift streaks of light.
From places south of the equator, the Eta Aquarids put on a very good show; Australians consider them to be their best meteor display of the year.
But for those watching from north of the equator, it's a much different story.
What's the point?
The radiant (the emanation point of these meteors) is within the "Water Jar" of the constellation Aquarius, which begins to rise above the eastern horizon around 3 a.m. local daylight time, but unfortunately, never really gets very high as seen from north temperate latitudes. And soon after 4 a.m. morning twilight will begin to brighten the sky.
So, if you're hoping to see up to 60 meteors per hour, forget it; with the radiant so low above the horizon, the majority of those meteors will be streaking below the horizon and out of your view.
In fact, from North America, typical Eta Aquarid rates are only 10 meteors per hour at 26 degrees north latitude (Miami, Florida or Brownsville, Texas), five per hour at around 35 degrees latitude (Los Angeles or Cape Hatteras, North Carolina) and practically zero to the north of 40 degrees (New York City, Chicago, and Philadelphia).
So, you might ask, "What's the point of getting up before dawn to watch?" The answer is you might still see something spectacular.
Catch an Earthgrazer
For most, perhaps the best hope is catching a glimpse of a meteor emerging from the radiant that will skim the Earth's atmosphere horizontally — much like a bug skimming the side window of an automobile. Meteor watchers call such shooting stars "Earthgrazers." They leave colorful, long-lasting trails which are extremely long and tend to hug the horizon rather than shooting overhead. They are also rarely numerous, but if you are fortunate to catch sight of only one or two it will make getting up and heading outside before the first light of dawn well worthwhile.
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 that 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."
So it is that the shooting stars that we have come to call the Eta Aquarids are really an encounter with the traces of a famous visitor from the depths of space and from the dawn of creation.
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.