Wednesday, December 08 2010 @ 04:46 PM CST
Contributed by: dgrosvold
In the evenings this week, Mercury remains in view low about the southwest horizon during twilight. Look about 40 minutes after sunset. Mercury fades from magnitude Ė0.4 to +0.1 this week.
As soon as it gets dark on Thursday evening, look for the waxing crescent Moon in the southwest. To the right of the Moon about 7°, is tiny Alpha Capricorni (α Cap.) If you have sharp vision you can barely see that this is a very close double star. You can resolve it easily in binoculars.
Jupiter still shines brightly this week at magnitude -2.5. Just after dusk on Friday evening look far to the lower right of Jupiter for the waxing crescent Moon. Look below Jupiter to the lower left of the Moon for Fomalhaut (FOAM-a-lout), in Piscis Austrinus, sometimes called “the Autumn Star.”
By Saturday evening, the nearly first-quarter Moon this evening forms a roughly equilateral triangle with bright Jupiter to its upper left and Fomalhaut to its lower left. The Moon reaches First Quarter at 7:59 AM CST, on Monday December 13th.
From now until December 13th, hourly rates increase until a peak of 50-80 meteors per hour is attained. The rate then tapers off until the last Geminids on December 18th, when the rates fall to one every hour or so. Meteor showers occur all the time, but most are very weak. So there may be stray meteors that are not part of the Geminids during this time as well. When you see a meteor, how do you know if it's a Geminid? Trace the path of the meteor back to its apparent origin. If that origin ends up being in Gemini or close to it, then it's probably a Geminid.
The best way to observe the Geminid Meteor Shower is lie back on a chaise lounge with a clear view of the sky toward Gemini. This time of year, be sure to dress warmly, get a thermos of coffee or hot chocolate, and maybe even throw on a blanket or two. As you lie there, look high up and all around the sky, and don't focus in just one place.
On a historical note, the Geminid meteor shower appeared suddenly in the latter part of the 1800's. R. P. Greg of Manchester in the UK first noted several meteors that had a radiant in Gemini in December of 1862. Several other observers independently discovered the same activity the same year from the United States.
Early observations in the late nineteenth century reported the hourly rates at about 14 per hour. As the century waned, the hourly rate seemed to increase to about 23 per hour, with many more bright meteors. These rates have continued to increase throughout the 20th century, averaging about 50 per hour mid-century with the peak rate reaching an average of 80 per hour in the 1980s. The peak hourly rate continues to remain at 80 per hour today. Scientists now think the Geminids are tied to the passage of an asteroid (or minor planet,) 3200 Phaethon, in our solar system across Earth orbit every few years. The Earth passes through the dust and debris left in its wake, creating tiny meteors in our upper atmosphere as we pass.