Friday, December 28, 2012

A little too slow for the lunar halo

I was taking Katie out to pee last night at 3:15am and saw my first lunar halo (at least the first since I started paying any real attention to the night sky). A lunar halo is an optical phenomenon in which hexagonal ice crystals form a 22° halo of light around the moon. The halo was very bright and obvious while I was out, but I didn't have my camera on me!!

Since the effect is atmospheric rather than astronomic, a few minutes makes a big difference. By the time I got my tripod out the icy clouds had all but moved on. I got this photo that shows a small arc around the right side - all that remained of the faint halo.

faint lunar halo
Faint lunar halo, a little too late!
This was a 10 second exposure. I don't think I needed to go that long because I've seen some great shots at ISO 200, 2.5 sec exposure time. Next time I'll know, and I'll be ready!

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