Moon and Regulus

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As winter begins to give way to spring here in the northern hemisphere, the days are getting noticeably longer -- a couple of minutes longer every day. In addition to the extra light and heat from the Sun, that also gives us an extra dose of ultraviolet energy -- the type of energy that causes sunburn and genetic mutations.

Fortunately, the Sun produces relatively little ultraviolet. Because of its temperature, most of the energy it beams into space is in the form of visible light.

But stars that are a good bit hotter than the Sun pump a lot of ultraviolet energy into space. One example is Regulus, the "heart" of Leo, the lion. It's to the lower left of the Moon as night falls this evening. The Moon moves closer to the bright star as they arc high across the south in late evening, and set in the west before dawn.

If you lined up Regulus and the Sun at the same distance, Regulus would look about 140 times brighter than the Sun does. But that only accounts for their visible light. Regulus is thousands of degrees hotter than the Sun, so it looks much bluer, and produces a lot more ultraviolet. So when you add up all the energy they produce, Regulus is about 240 times brighter than the Sun.

Because of all that energy, any habitable planet would be much farther from Regulus than Earth is from the Sun. But the planet would still get a massive dose of ultraviolet energy, making it an unhealthy place to live.

Script by Damond Benningfield, Copyright 2006, 2009

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