Sundog Near Sunrise

January 26, 2006


Provided by: Terry Reagan
Summary authors & editors: Jim Foster; Terry Reagan

On the morning of December 14, 2005, this chummy sundog appeared over Marcellus Falls, New York. A halo or sundog appearing near the surface may look a bit like a rainbow. However, the fact that this band of light was viewed looking east, 47 minutes after sunrise, is a key to its identification. Rainbows are seen at the antisolar point (opposite of the Sun) while halos and sundogs are observed in the vicinity of the solar disk -- most often about 22 degrees from the Sun. In addition, the color scheme is different for rainbows and halos. With a rainbow, the red color band is on the outside of the bow -- it's on the inside of a sundog or halo (closest to the Sun). Though the colors aren't usually as vivid in a sundog as in a rainbow, the refracted light from a sundog may be quite intense (see the Earth Science Picture of the Day for September 8, 2005). Ice crystals in cirrus clouds are typically responsible for halo formation, but in this case, the crystals were free falling through the lower atmosphere -- temperatures at the surface that morning were near 0 degrees F (-18 C).

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