Geminid Meteor Shower Puts On A Show This Week

Two Geminid fireball meteors appear to shoot from the constellation Gemini above Orion, hence their name. The Geminid meteor shower will climax on the night of Dec. 13-14. Credit: John Chumack
Two Geminid fireball meteors shoot from the constellation Gemini above Orion. The Geminid meteor shower will climax on the night of Dec. 13-14. Despite a full moon, the shower’s well worth watching. Credit: John Chumack

Every December the Geminid meteor shower roars to life. It’s now the year’s richest shower and can spitball up to 100 meteors an hour when observed under optimal conditions from a dark sky site. Let me be honest at the outset. This year’s shower will be compromised by none other than a supermoon. Yes! That bad boy’s back. No, it won’t be as super-duper as last month’s supermoon, but it will be larger and brighter than a typical full moon. The December full moon, known as the Cold Moon, wraps up a triad of supermoons that started in October.

The moon is a famous sky-brightener, with the full moon the worst offender. Instead of the expected number, we’ll probably see closer to a dozen an hour. But here’s the good news. The Geminids, along with the Perseids of August, have the greatest number of fireballs — really bright meteors — of any shower. That boosts your chance of seeing a few nice meteors despite moonlight.

The Geminids radiate from a point in the sky near the bright star Castor in the constellation Gemini the Twins, which is already up in the east by 9 p.m. The radiant is a perspective effect just like railroad tracks converging in the distance. As Earth plows into the stream of debris left by asteroid 3200 Phaethon, the particles burn up as meteors that appear to shoot from one point in the sky. Map: Bob King, Source: Stellarium
The Geminids radiate from a point in the sky near the bright star Castor in the constellation Gemini the Twins, which is already up in the east by 9 p.m. The radiant is a perspective effect just like railroad tracks converging in the distance. As Earth plows into the stream of debris left by asteroid 3200 Phaethon, the particles burn up as meteors that appear to shoot from one point in the sky. Map: Bob King, Source: Stellarium

Another factor on your side is timing. The Geminids emanate from a “radiant” in the constellation Gemini, which is well up in the eastern sky during mid to late evening hours. You can start watching as early as 9 p.m. I recommend getting under a sleeping bag in a comfy reclining chair and facing northeast or south. Avoid looking at the brilliant moon, so you can preserve as much of your night vision as possible. Save moongazing for either before or after the shower and then soak in those recycled solar rays to work on that moon tan. The later you stay up, the more meteors you’ll see with the peak occurring around 2-2:30 a.m. Dec. 14, when Gemini stands highest in the sky.

False color composite of the 2008 Geminid shower taken with an all-sky camera. Credit:NASA/MSFC/B. Cooke, NASA's Meteoroid Environment Office
False color composite of the 2008 Geminid shower taken with an all-sky camera. Lots of Geminids here but also a few sporadics. Credit:NASA/MSFC/B. Cooke, NASA’s Meteoroid Environment Office

Like all showers, the Geminids can be traced back to one point in the sky, the radiant. If you’ve driven through falling snow at night, your headlights will show that the snow appears to radiate from a point ahead of the car. Flakes near the “snow radiant” make short streaks; those off to the side make long streaks. The same happens during meteor showers when Earth plows through the debris left by comets and asteroids. As dust and bits of rock slam into our atmosphere, they also appear to radiate from a point ahead of us.

As you’re watching the shower, you’ll also see random or sporadic meteors. They’re easy to identify because they don’t point back to Gemini. Some 5-10 sporadics flare on a moonless night under a dark sky.

Asteroid (3200) Phaethon imaged on 25 Dec 2010 with the 37 cm F14 Cassegrain telescope of Winer Observatory, Sonoita (MPC 857) by Marco Langbroek.
Here’s the little guy behind the Geminids. It’s asteroid 3200 Phaethon which is just 3 miles (5 km) wide. These photos, taken on Dec. 25, 2010, show it inching through a star field. Credit: Marco Langbroek.

Most showers originate from comet dust. Dust sent whizzing off into space by solar heating when the comet approaches the sun hangs behind and circulates around the comet’s orbit. Each year, Earth’s orbit intersects the debris stream and for a day or three we get a meteor shower as the material strikes the atmosphere at high speed, burning up in the process. Meteors are really glowing tubes of air caused by the particle striking and exciting atoms and molecules. The molecules return to their “resting” states by giving off that extra energy in the form of light. A meteor!

Geminids are different from many meteor showers. Their “parent” is no comet but an asteroid named 3200 Phaethon (FAY-eh-thon). OK, to be fair, it’s sometimes called a rock comet because it’s one of those rare asteroids that occasionally spews streams of dust and rock particles. It’s these bits of slough that eventually become our beloved Geminids.

Good luck Tuesday night! If it’s cloudy, the 12th and 14th will also be OK for meteor watching, too. We’ve been nothing short of spectacularly cloudy in my town, so I’m game for anything.