Jimmy Westlake: Cancer the crab

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Jimmy Westlake

Jimmy Westlake's Celestial News column appears Tuesdays in the Steamboat Today.

Find more columns by Westlake here.

Of the 12 constellations that mark the Sun's annual path through our sky, called the zodiac, Cancer the Crab is the faintest and most challenging to locate. The Crab rides high in the sky on spring evenings, tucked in between the more prominent constellations of Gemini the Twins to the west and Leo the Lion to the east. Finding this celestial crustacean requires a dark, moonless night, so the middle two weeks of April this year are perfect for crab hunting since the new moon falls on April 17.

Greek mythology identifies this Crab as the pesky crustacean that was nipping at the toes of Hercules during his battle with the giant sea serpent, Hydra. Hercules crushed Cancer under his foot and the vindictive queen of the gods, Hera, immortalized the Crab in the stars.

It was here, in the constellation of Cancer, that the Sun reached its highest point in the sky marking the summer solstice back in the days of the Mesopotamian civilization; thus, the Crab lent his name to our Tropic of Cancer. Since that ancient time, the precession of the Earth's axis of rotation has shifted the Sun's highest point into the neighboring constellation of Gemini.

To locate the stars of Cancer the Crab, choose a dark, moonless night and look about midway between Gemini's bright stars Castor and Pollux and Leo's bright star Regulus. There you'll find a rather large fuzzy-looking patch of light with a little star on either side of it. This marks the carapace, or shell, of the Crab, but to the ancient sky watchers, this fuzzy spot was known as the Praesepe, or Manger. The two little stars that flank the Manger are named Asellus Borealis and Asellus Australis, the Northern and Southern Donkeys, apparently munching on the hay in the manger! Aim a small telescope or pair of binoculars at the Praesepe and you'll see why it is also known as the Beehive Star Cluster. Catalogued as the 44th object in Charles Messier's famous list of celestial fuzzballs, the Beehive Cluster contains several dozen stars delightfully arranged into little pairs and triangles. The numerous faint stars that surround the Praesepe mark the Crab's claws and legs.

This year, the bright yellow planet Saturn lies just beyond the reach of Cancer's pointy pincers.

Professor 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 websites 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. His "Celestial News" article appears weekly in the local Steamboat Pilot newspaper. He also records a radio spot called the "Cosmic Moment" for the local radio station "The Range" at 107.3 FM.

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