July 29, 2002
The photo above shows a brilliant parhelion or sundog, which because it was so bright was difficult to view directly. It's called a sundog since it faithfully follows the Sun, always remaining at its side, approximately 22 degrees from the Sun. The 6-sided ice crystals that form this phenomenon have a preferred orientation (they're aligned horizontally), unlike the crystals that compose the 22 degree halo, which are randomly oriented. These colorful bright patches of light often occur in pairs, one on one side of the Sun and one on the other. Note that the reddish color always faces the Sun. The inset shows the brightness and position of the sundog relative to the Sun. See also the Earth Science Picture of the Day for April 11. 2002.