Merope Nebula
 A thick cloud of dust around the Pleiades star cluster glows brightly in this false-color infrared image from Spitzer Space Telescope. The stars are lighting up the dust cloud, known as the Merope Nebula, as they pass through it. The stars and nebula are unrelated. [NASA/JPL/Caltech]
What isn't visible to the unaided eye is a hazy cloud around the stars. It's known as the Merope Nebula, and it was discovered by German astronomer Wilhelm Tempel 150 years ago tonight.
The nebula is named for one of the brightest stars in the Pleiades. Merope is a big, hot, heavy star that's already nearing the end of its life, even though it's only about a hundred million years old -- only a few percent the age of the Sun.
For a long time, astronomers thought the nebula was the gas and dust left over from the birth of the Pleiades, so the stars and nebula traveled through space together.
But fairly recently, they found that the stars and nebula are moving in opposite directions. In fact, the Pleiades leave a long wake behind them as they plow through the cloud. That means they aren't related at all -- they just happen to be passing by each other.
Light from the cluster's hot, blue stars reflects off tiny grains of dust in the nebula, lighting up the cloud. So long-exposure pictures show wispy streaks of blue surrounding the Pleiades.
Look for the Pleiades low in the northeast by around 9 o'clock -- a tiny but beautiful cluster of stars that's passing through a big cloud of dust.
Script by Damond Benningfield, Copyright 2009
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