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August 25, 2013

During his life, eighteenth-century French astronomer Charles Messier was known for the many comets he found. Today, though, he’s best known for a list he compiled of celestial objects that resemble comets. Messier’s catalog contains only about a hundred objects, but for the most part it’s a “Who’s Who” of the sky. It features such well-known sights as the Orion Nebula, the Pleiades star cluster, and the Andromeda galaxy.

But Messier's catalog also lists some obscure objects. A good example is number 18 on the list.

M18 is a small star cluster in Sagittarius, the constellation that boasts more Messier objects than any other. That’s because the center of the Milky Way galaxy lies within the constellation’s borders. So when we look at Sagittarius, we’re gazing toward the equivalent of galactic downtown.

M18 is about 4,000 light-years from Earth, and resides in the spiral arm that’s inward from ours. The cluster is much younger than the Sun. In fact, it’s so young that many of its hottest and most massive stars — the ones that burn out first — are still shining.

Sagittarius stands due south as night falls. It’s best known for a group of eight stars that outline the shape of a teapot. With the help of a star chart and binoculars or a telescope, you can find M18 standing well above the teapot. It’s not a dazzler — you may glimpse just a dozen or so of its stars. It’s a reminder that not every object on Messier's famous list is a celestial showstopper.


Script by Ken Croswell, Copyright 2013

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