For the week including July 16, 2010

ngc 6441 ngc 6302 M6 m7 ngc 6302 location M6 location M7 Location Antares Larger Illustration

THE STING

This week we’ll round out our exploration of the Scorpius, the Scorpion, with a tour of the business end of the constellation. Scorpius rises above the southern horizon after sunset and it’s one of the constellations that really looks like what it’s supposed to be. During the reign of Julius Caesar, the Scorpion’s claws were removed and made into the constellation of Libra, the Balance. But the rest of the Scorpion is still up there, right down to the stinger. The magnificent red-giant star Antares marks the heart of the Scorpion and because it’s the brightest star in the south, it makes Scorpius easy to find. The Scorpion’s tail has some interesting features and if you look toward it on a clear evening you should see a soft glow; unusual in that there doesn’t seem to be any stars there to give off light.

The light you are seeing comes from hundreds of light years away in the open star clusters M6 and M7. An open cluster is a group of stars that are associated through a bond of strong gravitational attraction. Some clusters contain a small handful of members while others may hold thousands. Because open clusters occur in the plane of our galaxy, their presence is often obscured by the tremendous amounts of gases and dust that can lie between stars. It has taken a clear line-of-sight to discover these clusters and the structure of our galaxy hasn’t been fully cooperative. Still, hundreds of these clusters have been cataloged by astronomers over the past two hundred years, and the famous glowing regions of M6 and M7 have appeared on star maps that date back more than two thousand years. Shown at upper left, M7 covers a larger part of the sky and contains around eighty stars notable for their color differences. It’s located nearly 800 hundred light years away and is over 250 million years old. M6, also called the “Butterfly Cluster”, is shown at the center left. It contains over 100 stars covering an area of some twenty light years. This cluster of has an estimated age of 100 million years and is filled with hot young stars. The glowing mist surrounding M6 is a reflection nebula often associated with star forming regions. Starlight scattering off of gases and dust causes the nebula’s distinctive color. The light that is directed towards us is shifted toward the blue end of the spectrum.

The Scorpion’s sting is marked by the stars G Scorpii (the brightest star in the sky without a common name) and Shaula (Arabic for “stinger”). Telescope owners can use these stars as guides to locating fainter objects in the constellation. At 136 light years away, the globular cluster NGC 6441 is a dense collection of several thousand stars. Shown in the Digitized Sky Survey at lower right, it’s nestled against G Scorpii in the evening sky. The Hubble Space Telescope photograph of NGC 6302 (also known as The Bug Nebula), shown at upper right, may represent the death throes of the elder member of a double-star system. Some astronomers believe its appearance suggests those pesky critters that splat into windshields on the highway.

The photographs of M6 and M7 are from the National Optical Astronomy Observatory.

Unless otherwise indicated, all content of this web site is the copyright of Robert Deegan and all rights are reserved.