Jimmy Westlake: Spot Sagitta in the Colorado night sky
August 24, 2011
Moonless nights of late summer are perfect for stargazing. The softly glowing band of the Milky Way arches across the sky like a colorless rainbow. The archer, Sagittarius, chases Scorpius across the southern horizon toward the west. The great bear, Ursa Major, sinks low in the northwestern sky just as the familiar "W" of Queen Cassiopeia's Chair rises in the northeast. To the east, Pegasus, the winged horse, is sailing up over the horizon while overhead the three prominent stars of the Summer Triangle twinkle brightly.
These three stars, Vega, Deneb and Altair, enclose within their three-sided box one of the smallest and oldest of our constellations, Sagitta the Arrow. Look for the four main stars of Sagitta near the southernmost tip of the Summer Triangle, just above the bright star Altair. Two stars form the shaft of the arrow, pointing east and another pair forms the feathered fletching behind.
The stars of Sagitta so convincingly suggest the shape of an arrow that virtually all of the ancient civilizations recognized it as such. It dates back to at least the 4th century B.C., yet no one can agree on who launched this arrow on its celestial flight.
One myth considers the arrow to be the one fired by Hercules to kill the eagle that tormented Prometheus, who was being punished by Jupiter for teaching mankind about fire. This story is supported by the nearby constellations of Hercules and Aquila the Eagle.
Another tale attaches the little arrow to Sagittarius the Archer, farther to the south. Indeed, Sagittarius is poised in the sky with arrow nocked and bow drawn and aimed at the Scorpion's heart. But if Sagitta represents a shot fired by Sagittarius at Scorpius, then this archer was way off the mark since the arrow is headed in the opposite direction!
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Sagitta is so small that you can easily fit the entire constellation within your binoculars' field of view. Look for the faint little fuzz ball of a star cluster called Messier 71, or M71, right between the two stars of the arrow's shaft. If you look Friday night, you'll notice a second fuzz ball right beside M71. You're not seeing double — it's this summer's little cosmic interloper, Comet Garradd, passing through the constellation.
If you would like to learn more about exploring Colorado's night sky with the naked eye and binoculars, consider signing up for my new one-credit course at Colorado Mountain College this fall, AST108 — Colorado Night Sky I. The class will run from 7 to 9:10 p.m. on seven consecutive Tuesday evenings, beginning Sept. 6. For more information, call the CMC office at 970-870-4444.
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 all around the world. Check out Jimmy's astrophotography website at http://www.jwestlake.com.