Wednesday, October 19, 2005

Astronomical Event Tonight

There is going to be a nifty little event tonight that you can observe with your binoculars.

The moon moves across the sky at a rate of 0.5 degrees per hour. The angular diameter of the moon is 0.5 degrees, so that means that the moon moves its full diameter across the sky once per hour. Normally, it's difficult to detect the moon's motion just by looking at it. However, when the moon rises tonight (around 8:30 PM), the Pleiades star cluster will be just above it. Use your binoculars to view the top portion of the moon along with the cluster -- you should be able to clearly see the moon's motion relative to the Pleiades' stars.

The Pleiades, or the "Seven Sisters," is an asterism that is often mistaken for one of the Dippers. You can see why

However, it's much smaller on the sky than either of the Dippers. This is closer to what the cluster looks like to the unaided eye

I'm gonna try to observe this tonight with binoculars and telescope. If anyone else decides to try, please let me know what you saw!

Update, 10/20/05: I did some observing with binoculars around 8:30 PM, but didn't get a good view because of the haze as the moon was rising. Managed to sit in a big puddle of water and tarry gravel trying to get a steady view. Grrr. However, I used a telescope (8" Dobsonian with 25mm eyepiece) about a half-hour later and managed to observe some movement. Whoopee!


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