It has been 26 years since Halley's Comet last passed through the inner solar system, by this weekend skywatchers have a chance to see leftover bits of the comet light up the night sky in the Orionid meteor shower.
The Orionid meteor shower can best be described as a junior version of the famous Perseid meteor shower and is scheduled to reach its maximum before sunrise on Sunday morning (Oct. 21). Patient night sky observers with clear, dark skies could see dozens of meteors an hour, according to NASA.
This will be an excellent year to look for the Orionids, since the moon will set around 11 p.m. local time on Saturday night (Oct. 20) and will not be a hindrance at all; so the sky will be dark for prospective meteor watchers right on through the first light of dawn early Sunday morning. [Photos: Orionid Meteor Shower of 2012]
The orbit of Halley's Comet closely approaches the Earth's orbit at two places. One point is in the early part of May producing a meteor display known as the Eta Aquarids.
The other point comes in the middle to latter part of October, producing the Orionids.
Orionid meteor shower: How to watch
Currently, Orion appears ahead of us in our journey around the sun, and has not completely risen above the eastern horizon until after 11 p.m. local daylight time. At its best several hours later, at around 5 a.m. — Orion will be highest in the sky toward the south — Orionids typically produce around 20 to 25 meteors per hour under a clear, dark sky.
Typically, Orionid meteors are normally dim and not well seen from urban locations, so we suggest that you find a safe rural location to see the best Orionid activity. Actually, Orionid activity started to increase noticeably on Oct. 17, when they started appearing at roughly five per hour.
After peaking on the morning of Oct. 21, activity will begin to slowly descend, dropping back to around five per hour around Oct. 25. The last few stragglers usually appear sometime in early to mid-November. [October's Best Night Sky Sights (Video)]
Orionid meteor shower: what to expect
The best time to see the Orionid meteor shower is anytime from about 1 or 2 a.m. local daylight time until around dawn, when the shower’s radiant (in Orion’s upraised club, just north of the bright red star, Betelegeuse) is highest above the southern horizon.
The higher the radiant, the more meteors appear all over the sky. The Orionids are one of just a handful of known meteor showers that can be observed equally well from both the Northern and Southern Hemispheres.
The Orionids are one of the better annual meteor shower displays, producing about 15 to 20 meteors per hour at their peak. Add the 5 to 10 sporadic meteors that always are plunging into our atmosphere and you get a maximum of about 20 to 30 meteors per hour for a dark sky location. Most of these meteors are relatively faint, however, so any light pollution will cut the total way down.
In recent years, this shower has been rather active for a few days before and after its Oct. 21 peak. Step outside before sunrise, for instance, on Saturday or Monday mornings and if you catch sight of a meteor, there’s about a 75 percent chance that it likely originated from the nucleus of Halley’s Comet.
"They are easily identified … from their speed," wrote David Levy and Stephen Edberg in "Observe: Meteors," an Astronomical League manual. "At 66 kilometers (41 miles) per second, they appear as fast streaks, faster by a hair than their sisters, the Eta Aquarids of May. And like the Eta Aquarids, the brightest of family tend to leave long-lasting trains. Fireballs are possible three days after maximum."
In fact, a dazzling fireball lit up the night sky over California on Wednesday night (Oct. 17), creating a brilliant light show and starting many witness with a loud sonic boom.
Recent studies have shown that about half of all Orionids that are seen leave trails that lasted longer than other meteors of equivalent brightness.
This is undoubtedly connected in some way to the makeup of Halley’s Comet. So it is that the shooting stars that we have come to call Orionids are really an encounter with the traces of a famous visitor from the depths of space and from the dawn of creation.
Halley's Comet takes roughly 75 years to circle the sun. But if you’re 30 years old or younger, you either have little or no memory of this famous cosmic vagabond (your next chance will come in the summer of 2061). Or maybe, if you were around back then, you didn’t see Halley at all because of light pollution or the comet's low altitude above the horizon.
That's what makes the Orionid meteor shower, and its partner the Eta Aquarids, so special: They give Earth a glimpse of Halley twice a year.
Comets are the leftovers of the day of creation, the odd bits and pieces of simple gases — methane, ammonia, carbon dioxide and water vapor — that went unused when the sun and its attendant planets came into their present form. All comets eventually disintegrate into meteor swarms and Halley’s is well into that process at this time.
These tiny particles – mostly ranging in size from dust to sand grains – remain along the original comet’s orbit, creating a “river of rubble” in space. In the case of Halley’s comet, which has likely circled the Sun many hundreds, if not thousands of times, its dirty trail of debris has been distributed more or less uniformly all along its entire orbit.
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.”
Meteoroids that are released into space from this cometary debris are the remnants of a comet’s nucleus. When they hit Earth's atmosphere, they flare up in bright meteors. Any pieces that reach the Earth are called meteorites.
Editor's Note: If you snapped any photos of the Orionid meteor shower and want to share them with SPACE.com, send the pictures, comments and location info to managing editor Tariq Malik at firstname.lastname@example.org.
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.