Thursday, December 13, 2007

Catch a moving planet (and maybe a meteor or two!)

Image Credit: Mouser Williams/Wikipedia

The word "planet" is derived from the ancient Greek word for "wanderer." Unlike stars, which appear in the same place relative to one another night after night, year after year, the planets move about in the sky, slowly drifting from one constellation to the next.

In modern times, most people have never seen a planet actually wandering. Well, now is your chance! Our target is Mars, the Red Planet.

This month, Mars is wandering near the constellation Orion. I've put a picture of Orion above -- it's a fairly easy constellation for most people to see, you can see it even in the glare of city lights, and it is made of bright stars. This month, Orion is sideways in the East at early evening, and then high in the southern sky for most of the night. See if you can find it! Of course, if you are in the Southern Hemisphere, Orion is upside down in the northern sky.

The planet Mars is north of Orion (higher in the sky for those living north of the equator). Mars will be the brightest thing in the sky this month (other than the moon or, if you are up early in the morning, Venus), so it's hard to miss. Mars is bright enough that you can probably notice it's reddish hue (or maybe more butterscotch than red). The star Betelgeuse in Orion (his upper-left shoulder in the picture above) is also reddish in color, but Mars is far brighter.

When you see both Mars and Orion, pay attention to where Mars is relative to Orion. Is it over his left or right shoulder? Or far to the left or right? Can you see other nearby star patterns that will help you remember where Mars is? Remember this placement. Then go inside and get warm and enjoy the evening.

A few nights later (or a week later or two weeks later, whenever it is clear next), go back an look for Mars again. It will have moved quite a bit (if you are looking in December, it will have moved to the west, or toward the right). I've been able to notice this difference in just a single night!

Once you've seen a planet move relative to the stars, you are one of the lucky few humans alive who has seen and recognized this motion. And what you are seeing is a delicate dance of the Earth and Mars around the sun -- the position of Mars is changing quickly this month because Earth is passing by Mars in our orbit -- we have the inside track around the sun, and are zipping right by pokey old Mars.

While you are outside, you may also see a meteor ("shooting star") or two. Today is the peak of the Geminid meteor shower, which produces about one meteor a minute in excellent conditions (so you could expect to see a couple if you are outside for 15 minutes or so).

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