entropy
archives
September 2007


3 Sep 2007 [link to here]
weird moon rising

I got up in the middle of the night last week and watched the eclipse. I saw a partial lunar eclipse when I was a kid and didn't think it was such a big deal. A little odd, but not spectacular like a solar eclipse. Last week's show was amazing though.

I watched for about two hours, from just before totality until just after, thin slivers of light on either end. The photos I've seen aren't very interesting. The moon, looking reddish. What really struck me was the whole scene. Normally, when you see the moon at night, it's brightly lit. Seeing a dim circle above a dark city was unearthly. The moon looked dead, and it was deeply unsettling. It looked like the sun had gone out. (Enjoy the long night of sex and drugs until the food runs out!)

Two hours sounds like a long time to stare at the moon, but I was surprised at how fast everything was happening. I set up an old telescope at around 40x magnification and the moon kept sliding out of view. I took some pictures, and at first I tried to get lots of light by using a longish (10-20 second) exposure. Eventually I figured out that the blurriness wasn't a focusing problem, it was motion blur. Even with a mere 135mm focal length (not nearly zoomy enough to see much lunar detail), I couldn't leave the shutter open more than a second or two without turning the stars into streaks and the moon into a featureless blob.

One could compute the maximum exposure time for a given focal length and set of viewing conditions to catch the moon without significant motion blur. I haven't found the answer worked out for me, but it wouldn't be too hard with the awesome Wikipedia entry on depth of field and some basic geometry.

It was also neat to see evidence of the moon's orbital motion in a relatively short span of time, and to verify that it really does go around in roughly the same direction as the earth spins.


24 Sep 2007 [link to here]
half baked

A phrase popped into my head tonight while a friend and I shared a big cookie: "Zeno's Finishing School". I guess that's where they teach the "take half the remainder" etiquette.