Circumhorizon Arc and Solar Halo

June 17, 2010


Photographer: Lisa Gonnelli
Summary Author: Lisa Gonnelli; Jim Foster

The photo above features a a colorful circumhorizon arc as viewed from Pilesgrove, New Jersey on May 7, 2010. This is the time of year (in the Northern Hemisphere) to observe these showy swatches since they can only be seen when the Sun is high in the sky – more than 58 degrees above the horizon. Circumhorizontal arcs appear approximately 46 degrees below the Sun. They form when sunlight traverses through hexagonal, plate-shaped ice crystals in cirrus clouds; light enters a vertical side face and exits through the lower horizontal basal face. When circumhorizontal arcs appear, there’s a good chance that solar halos and associated arcs may also be detected. Note the faint 22 degree halo near the top of this photo.

Photo details:
Camera Maker: OLYMPUS IMAGING CORP; Camera Model: E-500; Image Date: 2010-05-07 11:55:01 -0400; Focal Length: 17.0mm; Aperture: f/8.0; Exposure Time: 0.0050 s (1/200); ISO equiv: 100; Exposure Bias: none; Metering Mode: Matrix; Exposure: Creative Program (based towards depth of field); White Balance: Auto; Light Source: Unknown; Flash Fired: No (Auto); Color Space: sRGB