January 15, 2009—Like glowing parentheses, two sun dogs gave cold-bitten Omaha, Nebraska, residents a reason to go outside Wednesday.

Typically seen to the left and right of a low-lying sun, sun dogs, or parhelia, can take a number of forms—from slightly brighter segments of a solar halo (as shown) to rainbow-hued horizontal streaks to blinding spots nearly indistinguishable from the sun itself.

The sharpness, movement, and orientation of hexagonal, cloudborne ice crystals determine a sun dog's shape, sharpness, and color. Mottled, wobbling, or tall crystals, for example, generally result in more diffuse or colorful displays.

Despite Nebraska's subzero temperatures yesterday, sun dogs don't require cold ground temperatures. The atmospheric phenomena can be seen globally in any season—and even on other worlds. Eight-sided ammonia crystals above Jupiter and Saturn, for example, may spawn quadruple sun dogs, according to physicist Les Cowley on the Atmospheric Optics Web site.

See also: "Rare 'Fiery Rainbow' Spotted Over Idaho.

—Ted Chamberlain