The Geminid Meteors
Published on Dec 10, 2006 at 2:18 pm.
3 Comments.
Filed under meteors.
A little over a week ago, I posted about the asteroid Phaethon and its association with the Geminid Meteors. The Geminid Meteor Shower peaks early Thursday morning, December 14. The Moon will rise about 1:30 to 2:00am (depending upon your location), so there will be a few hours of good dark skies in which to see the meteors. Unfotunately for me, this is during final exams week! So, I’ll be pretty busy, and I won’t get a chance to leave the metropolitan area to get to dark skies. But, the Geminids often have enough bright meteors that if you can find a place with only moderate light pollution, you can see some meteors.
Predictions for this year’s Geminids are for a peak of about 120 meteors per hour, but that is for ideal conditions. Expect half of that for the average observer, but that is still a lot of meteors. In fact, in recent years, the Geminids have become one of the best of the annual meteor showers, and they have been steadily increasing in intensity. The average Geminid meteor is about magnitude 2.5, but there are a number of brighter ones mixed in. While the peak is the morning of the 14th, activity has already begun, and will steadiy increase until the peak. For a couple days before the peak, expect about 1/4 to 1/2 of the meteor activity of the peak. The shower has a sharp edge to activity, though, and activity drops off rather quickly afterwards, but a trickle of meteors remain for several more days, and the later ones have a higher proportion of brighter meteors, according to Neil Bone, the director of the British Astronomical Society’s Meteor Section.
The meteors appear to radiate away from the constellation Gemini, and hence the name Geminids. In partidular, they radiate away from the head of Gemini, near the stars Castor and Pollux. Interestingly, the path of the meteoroids is such that they hit Earth sort of on the side rather on the front. This means that activity starts before midnight for observers in the Northern Hemisphere (and a little after midnight for Southern hemisphere observers). Most meteor showers don’t start picking up activity for visual observers until midnight. For observers in the mid-northern lattitudes (most of the United States and Europe), activity will start becoming apparent two or three hours before midnight. The farther north that you are, the earlier the activity. For Canada and northern Europe, activity will begin as early as 8pm to 9pm. For the rest of us, it will pick up from 9pm to 10pm. For Mexico, activity doesn’t really get going until after 10pm.
The Geminids are a somewhat unusual meteor shower, even besides the early start to activity during the night. As I said in my earlier post the Geminids are associated with an asteroid (3200 Phaethon) rather than a comet, like most other meteor showers. The meteoroids are slightly denser than those of most meteor showers. This tends to mean that they take longer to burn up. Their orbits bring them to Earth with a closing velocity of only about 35km/s (a little slower than average for most meteor showers), and that, too, makes them take longer to burn up. The result is slightly longer meteor trails.
But, one more unusual things about the Geminids is how much the character of the meteor shower has changed since its discovery. The Geminids were first observed in the 1860’s. In 1877, the Geminids were reported to have a ZHR (zenithal hourly rate) of about 14. By the beginning of the 20th Century, that had risen slightly to about 20, where it remained for some time. But, then it began to climb. By the 1990’s the ZHR had risen to nearly 90. By 2000, the ZHR was near 100, and it is predicted to be about 120 this year. How can this happen? Well, it turns out that as the meteoroid swarm orbits the Sun, the gravity of the planets (mostly Jupiter, since it is the largest) shift the orbits slightly each year. Back in the 18th Century and before, the center of the meteoroid stream was passing so far inward of Earth’s orbit that the meteoroids pretty much missed Earth. Then, by the 19th Century, the swarm’s orbit had migrated close enough to Earth’s orbit that some of the meteoroids began hitting Earth. The center of the swarm is even closer now, and so activity has been picking up. Now, the Geminids are perhaps about the best meteor shower of the year. And, indidations are that the best may yet be to come. Shifting meteoroid orbits are nothing new. The Leonids are also subjected to shifts in orbit. In fact, after another century or so, there will be no more Leonid shower. Even now, it will be near the end of the 21st Century before another Leonid storm is possible, and then after a few more decent Leonid showers, they will be gone. But, the fact that the Geminids, are a fairly young shower, and a very good one, means that there may be other meteor swarms out there that do not currently intersect Earth’s orbit, but may do so in the future. So, who knows? Another spectacular meteor shower might happen any time.
If you want to go observe the Geminids, then the advice I gave for the Leonids works, with a little modification. If you live in the northern hemisphere, then go out a bit before midnight. The meteors that show up then are Earth grazers, and they tend to be a bit more spectacular than the later ones. Lay down on a lawn chair or blanket, and look up. The meteors will be shooting away from the northeast, but look towards the darkest part of the sky sort of overhead to see the best meteors. And have fun!
-Astroprof
A Ler…-- Rastos de Luz on December 11, 2006 at 11:42 am: 1
[…] “The Geminid Meteors“, no Astroprof’s Page. Elas começam a andar aÃ… […]
chenna reddy on November 29, 2007 at 3:37 am: 2
What are the chances to observe GMS for Indian observers, What is the moon’s position on this days, what are the best days to observe ?
Astroprof’s Page » 2007 Geminid Meteors on December 3, 2007 at 8:46 pm: 3
[…] Near the middle of every December we get the Geminid Meteor shower. I wrote about the Geminids last year, but they are one of the year’s best meteor showers, so they are worth writing about again. […]