SCIENTIFICS – SKY TALK – DECEMBER, 2017
Were I to pick my favorite of the year’s several good annual meteor showers, it wouldn’t be the famed Perseids of August (seemingly everyone’s favorite) but rather the Geminids of December. It consistently offers more “shooting stars” than any other display—typically at least 100 per hour, and occasionally as many as 120 or two every minute at its peak! And this year the Moon will essentially be out of the way, insuring dark skies.
We frequently emphasis meteor showers in this column and with 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. Nothing is as thrilling 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. The best hours to begin observing the display will be around 10 p.m. on the former, and then continuing into the morning hours. The meteors will appear to radiate 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 of the radiant helps make the Geminids so special to sky watchers: those
of most showers lie below the horizon during the evening hours. But in this case it’s already well up and you’ll see meteors streaming outward from it, with their numbers steadily 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 celestial objects themselves rising. This includes the Sun and Moon, as they dramatically seem to pop-up into the sky from out of nowhere.
There’s a subtle but fascinating reason why meteor showers 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 essentially 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 the dawn twilight interferes, which is when the impact-effect is at its maximum. Their higher velocity also makes those that are seen in the morning hours brighter than in the evening.
— 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.