The last day of 2011 was beautiful here in south Florida. Started off cool (chilly, even), but warmed nicely throughout the day. Since it was the first Saturday after Christmas, I was out in the field on the West Palm Beach Christmas Bird Count, and the weather proved mildly conducive to the birds we were seeking; a morning’s work yielded 50 species in some pretty marginal habitat. I’ll have more on the bird count later.
I spent the afternoon at the beach with Eric, who decided that a dead-tired-from-birding Daddy had no excuse not to take him, and I’m glad we went. The weather was just so lovely; much nicer than the previous two times we’d gone, with 20-mph easterlies howling at us, sending sand stinging against our legs and into our eyes. I actually wore my parka the last time I went to the beach!
But December 31, 2011, was absolutely idyllic:
Just perfect for building castles in the sand.
All was well until the evening, when I decided to haul out my big telescope and take a few pictures of the moon, which was nearing first quarter. It turned out that the hand controller for the computerized mount wasn’t working, so I couldn’t use the big mount and its tracking capability. I suspected that the battery was undercharged, so I hauled it into the garage, but by the little strap instead of by the battery box handles. And that was a huge mistake. I don’t think I’ve ever seen swelling in my shin bone quite so drastic or immediate. Two gigantic lumps and a divot where the battery came crashing down on my leg; I’ve been limping slightly ever since.
But on New Year’s Day, I couldn’t resist using my grab-and-go setup to get the first quarter moon on the first day of the year:
I haven’t gotten all the camera settings exactly the way I want them, but I really don’t notice the missing 2 megapixels from my “downgrade.” Do you? The picture’s a little grainy, but it’s because I had the ISO set to 400 to compensate for the fact that I didn’t have a tracking mount.
With a nontracking mount, there just isn’t enough light from the first-quarter moon to shoot the way I’m accustomed to, after two years of tracking the full moon. After all, when the moon is full, there’s enough light that I can shoot at ISO 64 and not get too much grain.
But with only half the moon’s lit surface to work with, the reduction in luminosity is enormous: first quarter moon is only 8% as bright as full moon. Put another way, it’s 2.7 magnitudes less bright ( −10 instead of −12.7). Put yet another way, it’s about a 12× reduction in brightness. (Numbers seem funny when you’re dealing with magnitudes because each step in magnitude, represented by a whole number, is not a unit increase, but a logarithmic one. A 1st-magnitude object is more than twice as bright [2.512× to be precise] as a second-magnitude object. And because the moon is an extended object, not a point source of light, the numbers get even funnier, but I’m not sure how, so I can’t explain them. This post was supposed to be just a snapshot of the first quarter moon to show off the new camera, but I got sidebarred—er, sidetracked.)