Lunar Halo Above Roswell, Georgia

December 04, 2010

Photographer: Thomas Faber
Summary Author: Thomas Faber; Jim Foster

The photo above showing a conspicuous 22-degree halo around the Moon was captured near Roswell, Georgia on October 24, 2010. The Moon was approximately one day past full. Halos result when hexagonal ice crystals in cirrus clouds are randomly oriented or are only weakly aligned. Notice the dark area within the halo, which is akin to the darkened region between the primary and secondary rainbows -- Alexander's dark band. Because no rays of moonlight (or sunlight) are refracted less than about 22 degrees, the sky inside the halo is clearly darker than outside it.

Photo details: Camera Maker: Canon; Camera Model: Canon PowerShot SX100 IS; Focal Length: 6.0mm; Aperture: f/3.2; Exposure Time: 15.000 s; ISO equiv: 100; Exposure Bias: none; Metering Mode: Matrix; White Balance: Auto; Flash Fired: No; Color Space: sRGB.