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The Question

(Submitted February 07, 1997)

I was wondering if you knew the names of the Sun dogs and moon dogs?

The Answer

Sundogs and moondogs are the names given to rainbow-like patches sometimes seen on either side of the Sun or the Moon. They are not real dogs and do not have names as far as I know. They are similar to the ring sometimes seen around the Moon.

Sundogs and the ring around the Moon are caused by the focused reflection from ice crystals in the upper atmosphere. Since the ice crystals are hexagons, the distance the sundogs are from the Sun and the radius of the ring around the Moon are always the same size in the sky (22 Degrees).

Many cultures hold the ring around the Moon as a sign of good luck, since it associated with good rainfall and healthy crops.

You can see a picture of Sundogs on the WWW at:

http://www.astropix.com/HTML/G_SUN/SUNDOGS.HTM

Thanks for your interest,

Jonathan Keohane (with help from much of the Ask an Astrophysicist team)

Questions on this topic are no longer responded to by the "Ask an Astrophysicist" service. See http://imagine.gsfc.nasa.gov/docs/ask_astro/ask_an_astronomer.html for help on other astronomy Q&A services.

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