Circumhorizontal Arc Over Yalaha, Florida

September 12, 2010

: Carol Waldvogel
Summary Author
: Carol Waldvogel; Jim Foster

This spirited circumhorizontal arc (CHA) seemed to be almost directly over my house in Yalaha, Florida. It was taken near noon on August 31, 2010. CHA's form in hexagonal ice crystals, found in cirrus clouds, when sunlight enters one of the crystal's vertical side faces and is refracted through the lower horizontal basal face. However, they can only be observed if the Sun is positioned more than 58 degrees above the horizon, which confines seeing them to the summer season at most mid-latitude locations. Note, always use caution when looking in the direction of the Sun.

Photo details: Camera Maker: PENTAX Corporation; Camera Model: PENTAX K10D; Focal Length: 50.0mm (35mm equivalent: 75mm); Aperture: f/8.0; Exposure Time: 0.0005 s (1/2000); ISO equiv: 100; Exposure Bias: none; Metering Mode: Center Weight; Exposure: aperture priority (semi-auto);White Balance: Auto; Flash Fired: No; Color Space: sRGB.