Thursday, August 11, 2005

Tha Moon Rulez!

I'm pretty sleepy today. Yesterday I awoke in Brevard, North Carolina, and slept in Dallas, Texas. This required a hefty drive during the intervening time, which meant that I didn't arrive at my bed until well after 2AM. Add to that the lingering effects of too much caffiene consumed in the later stages of the drive, and that sort of weird effect where you get so tired that you're too uncomfortable to sleep, and I didn't get much sleep last night.

The drive across Arkansas took me through the hours between dusk and midnight, and this afforded me an opportunity to observe the moon. As the sunset faded, and the stars began to shine, the waxing moon formed a solid cresent in the western sky. Immediately below its tip was a small star, just bright enough to see through the glow surrounding the moon. Being somewhat bored now, as I was a good ten hours into the drive home, I hit upon an idea for a little astronomical experiment. Stars, of course, are relatively fixed in the sky. They move only with the rotation and revolution of the earth. The moon, however, is in orbit around the earth, so it is moving through the sky in its month-long orbit. Therefore it might be possible to see the motion of the moon relative to the star over the course of the evening.

The moon is approximately 1/2 of one degree in angular width, and the star was approximately 1/4 of the width of the moon away from the tip of the crescent when I first noticed it, along a line through the two horns of the crescent. Over about two hours, the star appeared to lie along a line tangential to the moon's edge, parallel to the line through the two horns of the crescent. (If I could draw a diagram and get it on here easily, I would, but it would be a bit of a pain.) So the moon moved approximately 1/4 of a degree relative to the star. Now, the moon orbits the earth in 28 days, or 672 hours. In doing so it traverses a full 360 degrees. This means that the moon should move approximately 1/2 of a degree per hour. I'm a little disappointed that I couldn't get my observed moon motion to match up with my back-of-a-napkin estimation the lunar orbit. If anyone wants to check my math, feel free. But quantitative results aside, it was really cool to observe the motion of the moon.

In other news, the NC trip was good. I rained pretty much every day I was there, but it was still a welcome change from August in Dallas. And a welcome change from working. I really really hate being left in charge.

No comments: