Celestial News: The dippers of spring
Steamboat Springs — The celestial Bears, Ursa Major and Ursa Minor, are coming out of their winter hibernation and can be seen parading around the north celestial pole this month. Better known in the USA as the Big and Little Dippers, these star patterns are recognized and loved by all.
The seven bright stars that form the Big Dipper shine prominently above the northeastern horizon as darkness falls in March. It looks as if the Big Dipper is balancing precariously on its bent handle.
From top to bottom, the seven stars of the Big Dipper are named Dubhe, Merak, Phecda, Megrez, Alioth, Mizar and Alkaid.
Dubhe and Merak, the two stars at the top of the Big Dipper’s bowl, are nicknamed “the Pointer Stars” because a line drawn through the two stars and extended downward will lead you to our North Star, Polaris. Polaris is about as bright as the stars in the Big Dipper and is important because it lies very close to the north pole of the sky, called the north celestial pole.
As the Earth spins on its axis, the celestial sphere seems to pivot around the north celestial pole with Polaris positioned near the center of the bull’s eye. It remains nearly fixed in our sky, so it can always be relied on to point out the direction north for us.
Polaris also happens to be the star at the end of the handle of our Little Dipper. Like its bigger brother, the Little Dipper is composed of seven stars, although only two of the seven are prominent, Polaris and Kochab.
Moving down the handle in order from Polaris, the names of the remaining stars are Yildun, Epsilon, Zeta, Eta, Pherkad and Kochab. Together, Kochab and Pherkad are nicknamed “the Guardians of the Pole” because they circle the pole star Polaris as if protecting it from harm.
The four stars that make up the Little Dipper’s bowl are very conveniently and quite by chance classified as second, third, fourth and fifth magnitude stars. For comparison, a sixth magnitude star would be a star just at the limit of visibility to the human eye.
One can judge the clarity of the night sky and/or the degree of light pollution by noting how many of the Little Dipper’s bowl stars can be seen. If the sky is dark and clear, all four stars in the bowl should be visible. Unfortunately, from many urban and suburban areas, the two or three fainter stars are rendered invisible by artificial lighting that needlessly points upward and pollutes our night sky.
During the early spring, the two Dippers are positioned such that the Big Dipper appears to be pouring its contents into the Little Dipper below it. Perhaps the overflowing bowl of the Little Dipper is responsible for the April showers that rain down on us and bring the May flowers that we all enjoy.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His “Celestial News” column appears weekly in the Steamboat Today newspaper and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Check out Jimmy’s astrophotography website at http://www.jwestlake.com.
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