Sunday, March 29, 2015

Ringy Dingy!

We've had cloudy skies most of the day, and also have a 10-day-old gibbous Moon tonight, so figured I had little to no chance of coming up with a blog post, but what do you know - stepped outside to pick up cat food bowls and found a really nice ring around the moon!

This 22 degree halo is caused by moonlight (or sunlight during the daytime) refracting through two surfaces of hexagonal ice crystals in the clouds. Longer wavelengths are refracted a little less, so the inside of the halo shows a red fringe. This is an 8 second exposure with wide angle zoom set to 14mm, and really approximates the visual appearance pretty well. Ain't optics wonderful!?

Fortunately it is clear enough to see a few other objects along the red-fringed ring and moon. Brilliant Jupiter is up at the 10 o'clock position from the moon, and there are a few stars too. At left just inside the ring at 8 o'clock is Regulus, the brightest star in Leo, and also just inside the ring at 3 o'clock is Procyon (Alpha Canis Minoris). At the top of the image, splitting the ring are Castor and Pollus (top to bottom), in Gemini. Just in case you can't see all that, I'm providing a labeled version at right. I lucked out to find an astronomy-themed subject tonight - yippee!

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