Moon, Mars, and Regulus

StarDate: December 6, 2009

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Many ancient cultures envisioned the night sky as a great dome. The stars were seen as lights attached to the inside of the dome, or as pinpricks in its surface that allowed the light of heaven to shine through. In this cosmology, everything in the night sky except the Moon was the same distance from Earth.

The night sky isn't flat, though. It's really a three-dimensional canvas, with the visible stars stretching hundreds or even thousands of light-years away.

A good example of that depth is on display early tomorrow, as the Moon teams up with the planet Mars and the star Regulus. They're high in the sky at first light, with Regulus to the upper left of the Moon, and bright orange Mars a little farther to its upper right.

The Moon is the closest member of the trio, at a distance of about a quarter-million miles.

Mars is about 350 times farther than the Moon, at a distance of about 85 million miles. At that distance, it takes almost eight minutes for light from the planet to reach Earth.

Yet that great gulf is a mere hop away compared to the distance to Regulus, which is five and a half million times farther. At that range, it takes almost 80 years for Regulus's light to reach Earth. So keep in mind that the light you see from Regulus tonight has been traveling for a long time -- since around the start of the Great Depression.

Script by Damond Benningfield, Copyright 2009

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