Thursday, December 13, 2007



The Geminid meteor shower, which usually peaks each year between December 12th and December 14th, is the most reliable and spectacular of the annual meteor showers even though observation is less comfortable than that of other showers such as the summer Perseids. On the other hand the skies are usually clearer in winter than at other times of the year. This year the predicted peak will occur at 16:45 GMT on December 14th. This is 10:45 here in Winnipeg in the CST zone. Consult the Time and Date.Com website for the equivalent time in your locality. Time and Date also gives the times of Sunrise/sunset and Moonrise/Moonset as well as a weather forecast. This year the Moon will not interfere with viewing as it is a thin waxing crescent that sets at 8:18 pm. The expected peak time will unfortunately occur during daylight, but a large number of meteors are likely to be visible tonight, especially in the early morning hours, or tomorrow night. The Geminids have a rather extended peak so that viewing doesn't depend on getting an exact time. All weather reports, whether from Time and Date, from Environment Canada or from the Clear Dark Sky website, indicate good clear viewing conditions tonight but overcast tomorrow night. The Clear Dark Sky site has a wealth of other useful information as to viewing conditions for a vast number of locations in North America.

The Geminids are a rather recent meteor shower, having first been observed by astronomers R.P. Greg, B.V Marsh and A.C. Twining first observed them. They were observed again in 1863 by A.A. Herschel. It was only during the 1870s that astronomers realized that a new annual shower was underway. The Geminids gradually increased in intensity during the last century. This year there may be as many as 120 meteors visible per hour near the peak period. Intensity will decrease only slightly from 6 to 1o hours on either side of the peak. The intensity increases gradually in the 2 to 3 days prior to the peak and then falls off rapidly. Thus tonight should be a good time for viewing, specially after 2:00 am when Gemini is high in the sky (the number of meteors visible is largest when their radiant approaches the zenith).
The meteors of the Geminids are of medium speed, approaching Earth at about 35 kilometers per second. They are bright and usually white in colour, and are often productive of some spectacular fireballs. Their apparent speed is slow, and they can sometimes been seen to have jagged paths and to seemingly split. They leave few visible trails however. The radiant will come from a point just to the northwest of Castor, the upper star in the constellation (see diagram above). The Geminids are rather unique in that they originate from an earth-crossing asteroid, 3200 Phaeton, unlike other meteor showers which originate from cometary debris. This parent body was discovered as recently as 1983 by S. Green and J.K. Davies, using the Infrared Astronomical Satellite. This year Phaeton will be making its closest approach since 1983, coming within 11 million miles of Earth. There is some dispute about the nature of Phaeton as some believe that it is not an asteroid but rather the burnt-out nucleus of a comet.
So look to the northeast early this evening, and higher in the sky later to find Gemini, and happy frigid viewing. Have a look out for Mars as well. It shines brightly at the right-hand side of Gemini as it merges into Taurus. But more on Gemini and Mars later.


Gutenberg said...

The Guardian's science blog is trying to get together people's pictures and video of the Geminids

Mollmew said...

Space.Com often gathers such things, but I don't think they are doing so this time around. When I post again tomorrow about Gemini and Mars I'll try and give further references. For now I did a quick search on "astrophotography guides" and came up with the following interesting references for beginners like Molly.
Tim Printy's Astrophotography Tips
A Beginner's Guide to Astrophotography

As for Molly here in Winnipeg, she is not the best photographer in the world. So I'm not even going to try. The windchill here is now about 35 below- due to dip into the negative 40s by tomorrow. I duck out periodically during the night to look up to Gemini, but the whole idea of sitting and waiting with a camera with my limited skills hits me like a hammer. Let the braver(or those in more clement conditions) do it.