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Rings Around the Moon

March 29, 1976 / Glenn Shaw

Have you ever seen a ring around the moon? Folklore has it that this means bad weather is coming--and this particular "old wives tale" happens to be true.

The ring that appears around the moon arises from light passing through six-sided ice crystals high in the atmosphere. These ice crystals refract, or bend, light in the same manner that a camera lens bends light. The ring has a diameter of 22 , and sometimes, if you are lucky, it is also possible to detect a second ring, 44° diameter.

How can rings around the moon be used as a weather predictor? The ice crystals that cover the halo signify high altitude, thin cirrus clouds that normally precede a storm front by one or two days. Maybe the ancients knew more than we think they did.

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Since it was established by an Act of Congress in 1946, scientists at the Geophysical Institute have studied geophysical processes from the center of the Earth to the surface of the sun and beyond, turning data and observations into information useful for state, Arctic and national priorities.

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