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Moon and Company

October 27, 2013

The Moon has a couple of prominent companions in tomorrow’s pre-dawn sky. The star Regulus is close to the lower left of the Moon, with the orange planet Mars a little farther in that direction.

Regulus actually consists of four stars that are gravitationally bound to each other. But only one of them shines brightly enough to see with the unaided eye. That star is several times bigger and heavier than the Sun. And at optical wavelengths — the form of light that’s visible to our eyes — it’s about 150 times brighter than the Sun.

Regulus is thousands of degrees hotter than the Sun, though, so much of its light is in the ultraviolet — wavelengths that are invisible to the eye. When you add that to the visible light and all other wavelengths, the star is close to 400 times brighter than the Sun.

Most of the ultraviolet is blocked by Earth’s ozone layer, so it never reaches the surface. That layer also blocks most of the ultraviolet light from the Sun, which is a good thing for us. Ultraviolet causes sunburn and skin cancers, and can produce genetic mutations. So an unfiltered bath of solar UV wouldn’t be pleasant.

To study the ultraviolet light from the stars, astronomers must loft their telescopes high above the ozone layer — into Earth orbit or beyond. From that perch, they get an unobstructed view of the ultraviolet light of many objects — including brilliant stars like Regulus.

More about the Moon and Mars tomorrow.


Script by Damond Benningfield, Copyright 2013

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