Jimmy Westlake: The Via Lactea

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Now that the full moon is out of the sky, the dark summer sky reveals one of its most spectacular treasures -- the soft, misty glow of the Via Lactea, or the Milky Way. Contrary to what the ancient Romans believed, the Milky Way is not made of milk. It is the combined light of billions of distant suns, unresolved by the unaided eye. If you look through a pair of binoculars and sweep slowly across the Milky Way, you will rediscover what Galileo found in 1610 -- a multitude of faint stars. The situation is similar to flying over a sandy beach and seeing the white sand stretch for miles, yet you cannot see the individual sand grains that make up the beach.

The Milky Way is our home galaxy, a spiraling collection of hundreds of billions of stars more or less like our sun. Because it is flattened like a pancake and because we peer outward from within that pancake, we see the spiral arms wrapped gently around us in a narrow band that runs almost north to south on summer evenings.

Look closely and you'll notice that the band of the Milky Way seems to split into two parallel branches just south of the familiar Summer Triangle of stars Vega, Deneb and Altair. In reality, this Great Rift in the Milky Way, as it is known, is caused by an enormous cloud of opaque dust and gas thousands of light years away. The cloud blocks our view of the stars beyond.

Experiencing the subtle beauty of the Milky Way has become a privilege that many Americans will never have. A large percentage of our nation's population lives in or near a large city, where human light pollution drowns out this natural wonder. To them, the Milky Way is something that you read about in a book or see pictures of in a planetarium. Streetlights and spotlights aimed skyward scatter so much unnecessary light into the night sky that it overwhelms all but the brightest stars. Many cities, including Aspen, are making efforts to curb this urban light pollution to preserve the beauty of the nighttime sky. For the time being, at least here in Northwest Colorado, all we have to do is step out in our backyard to see the galaxy of which we are a part -- the majestic Milky Way.

Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. He is an avid astronomer whose photographs and articles have been published on the Web sites of CNN.com, NASA's "Astronomy Picture of the Day," Spaceweather.com, Space.com, Discover.com, and in Sky & Telescope, Astronomy, Night Sky, Discover, and WeatherWise magazines.

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