Celestial News: Behold the Great Dark Horse
Once the lingering twilight of late spring fades away, you can see the misty star clouds of the Milky Way arching across the sky, from the northeast, all the way to the south.
The band of the Milky Way that we see from earth is only a small portion of our vast Milky Way galaxy, a spinning collection of hundreds of billions of suns. The glowing star clouds that we see at night are composed of myriad suns, too distant and too faint for us to distinguish as individual stars without a telescope.
I like to compare it to flying over a stretch of white, sandy beach. From the air, you can see the band of white below, stretching in both directions. You know that it’s made of millions of individual sand grains, but from that distance, you can’t see the sand grains, just the white blanket that they form due to their sheer numbers.
The band of the Milky Way is like a beach made of stars.
If the night is dark and clear, you also can detect a network of dark clouds and tendrils meandering through the bright star clouds of the Milky Way. These dark patches are vast interstellar dust clouds, thousands of light years away. They gather in the space between the stars and effectively hide the light of the more distant suns behind them.
Astronomers once thought that these patches of missing stars were empty voids, allowing us to peer through the Milky Way and into the deep universe beyond our galaxy. It wasn’t until the opening years of the 20th century that American astronomer E. E. Barnard recognized that these dark regions were opaque clouds of interstellar dust, not open windows to the universe.
During the dark of the moon this month, you can see something truly wonderful — the elusive Great Dark Horse nebula in the Milky Way. The Great Dark Horse is not made of stars, like other constellations, but instead is made from the absence of stars. He is composed of a collection of dark, dusty nebulae that form the silhouette of a black stallion, reared back on his hind legs, against the bright star clouds behind him.
Under clear, dark sky conditions, you can see the Great Dark Horse with your naked eye. In fact, optical aid renders the Dark Horse invisible. He is big — about as large as your fist held at arm’s length — and hides in the patch of Milky Way between the fishhook pattern of Scorpius the Scorpion and the teapot pattern of Sagittarius the Archer.
His prominent dark hindquarters stand out in sharp contrast against the bright star clouds of the Milky Way. Look above the southern horizon about one-third of the way up to the zenith around midnight in early June and around 10 p.m. in late June.
If you don’t spot him at first, keep looking. Searching for dark constellations is similar to taking an ink-blot test. Once you see him, you’ll wonder how you ever overlooked something so obvious. He only comes out during the darkest of nights, so now is your chance to see the sky’s best-known dark constellation, the Great Dark Horse.
For information about astronomy-related events in Steamboat Springs, including public star parties at CMC’s Ball Observatory, contact physics and astronomy instructor Paul McCudden, at email@example.com or 970-870-4537 or visit the SKY Club web page at http://www.coloradomtn.edu/skyclub.
Jimmy Westlake is adjunct professor of Physical Sciences at Colorado Mountain College and former director of the Rollins Planetarium at Young Harris College in Georgia and the St. Charles Parish Library Planetarium in Luling, Louisiana. His Celestial News column appears monthly in the Steamboat Pilot & Today. Check out Westlake’s astrophotography website at http://www.jwestlake.com.
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