Moon and Company

StarDate: March 9, 2009

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The Moon and a couple of bright companions paint a pretty picture tonight. They stairstep up the eastern sky at nightfall, and sail across the south during the night.

Regulus, the brightest star of Leo, the lion, stands above the Moon as darkness falls, while the planet Saturn is a little farther to the lower left of the Moon. Saturn is brighter than Regulus right now, and it has a slightly warmer color.

Despite appearances, though, Regulus is actually the warmer of the two bodies. That's because it's a true star -- a giant ball of gas that produces energy in its core. As the energy works its way to the surface, it heats the layers of gas, causing the gas to glow. The surface of Regulus is thousands of degrees hotter than the Sun, so the star shines white, with perhaps a hint of blue.

Saturn, on the other hand, is a planet -- a relative to our own Earth. It has a solid core surrounded by layers of gas. But Saturn isn't nearly massive enough to shine as a star. Instead, sunlight strikes the planet's upper atmosphere and is reflected back into space. Ammonia, water vapor, and other compounds in the atmosphere give Saturn a slightly golden color -- a color that looks warm, even though the atmosphere itself is frigid.

Saturn looks especially warm right now because it's putting in its best showing of the year. It rises at sunset, remains visible all night, and shines brightest for the year.

More about Saturn and the Moon tomorrow.

Script by Damond Benningfield, Copyright 2009

For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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