Last year’s annual Geminid Meteor Shower was as perfect as it can get, with its late evening peak viewing time and absence of moonlight to brighten the sky. Unfortunately, a lot of the country was under a wintry overcast and the display clouded out for many skywatchers. But this month we have another opportunity to see again it under good conditions—and better yet, two evenings to watch for shooting stars in case one of them is overcast!
Readers may have noticed that we frequently emphasis meteor showers in this column. And for good reason. Watching shooting stars requires no optical aid at all—just a clear night with little or no moonlight to interfere with visibility and a good view of the sky. And nothing so excites as the sudden appearance out of the darkness of a bright meteor with its train of debris as it burns up in the atmosphere. This year’s Geminid Meteor Shower will be no exception. It reaches maximum activity on the late evening of December 13th into the morning of the 14th, and then again on the evening of the 14th into the morning of the 15th. This dual opportunity happens because the actual peak occurs during daylight between the two dates for most viewers.
The best hours to begin observing the display will be around 10 p.m. on the 13th and then continuing into the morning hours. The Moon will be in its waxing crescent phase and set early enough in the evening to leave a dark sky for the rest of the night. As one of the year’s richest displays, the Geminids are always well worth watching. Typically as many as 60 meteors per hour—or one a minute on average—can be seen during peak activity under good conditions. They appear to radiate or “shoot” from near Castor, one of the two bright “Twin Stars” (the other being Pollux) marking Gemini. To find them, set your Scientifics Star and Planet Locator for about 10 p.m. and face east, where you’ll see the pair about halfway up the sky. This early rising is what makes the Geminids so unique: the radiants of most showers lie below the horizon during the evening hours. But in this case the radiant is already well up and you’ll see meteors streaming outward, with their numbers increasing as the night grows later and Gemini climbs ever-higher. (Note that it’s actually the horizon “setting” or dropping as the Earth spins ever-eastward rather than sky objects themselves rising, including the Sun and Moon appearing to come up.)
As to why meteor showers seem to increase in activity towards dawn, during the evening hours we’re on the side of our planet “facing away” from the direction the meteors are approaching, so they have to “catch up” with us. But after midnight we’re turned into the direction of the radiant, causing them to slam into the atmosphere at much higher speeds. This results in many more meteors being seen right up until morning twilight interferes, which is when the impact-effect is at its maximum.
— James Mullaney
Former assistant editor at Sky & Telescope magazine & author of nine books on
stargazing. His latest, Celebrating the Universe!, is available from HayHouse.com.