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The Sky this Week, December 13-20

“The Sky This Week” appears every Tuesday. It is written by Ian Clarke, Director of the Hatter Planetarium at Gettysburg College.  The planetarium offers regular educational presentations about the stars and the skies; there’s something for early elementary through adults. Field trip requests are welcome. NOTE: field trip request form for 2022-23 is now live. Shows have concluded for Fall 2022, but we will post the schedule for the next semester around the new year.

Over the next few weeks, I’d like to focus on some of the bright stars and constellations of the winter skies. First up, Orion. This month you’ll find it after dark in the southeast. Classically it depicts a hunter with a belt and sword. The four bright stars that make up the main rectangle are, clockwise from top right, Bellatrix, Rigel, Saiph, and Betelgeuse. Rigel, a blue supergiant 860 light years away, is the brightest. It makes an excellent color contrast with reddish Betelgeuse at the opposite corner. Betelgeuse, a red giant nearing the end of its lifespan, varies in brightness slowly over months from almost as bright a Rigel to noticeably fainter. In early 2020 it became unusually dim for a period of several weeks. Astronomers currently believe that happened because the dying star ejected matter that later condensed into an obscuring dust cloud. Processes like this in giant stars seed the universe with the heavier elements that make up planets, and life!

december
Ian Clarke1
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Ian Clarke is the director of the Hatter Planetarium at Gettysburg College. In addition he has taught introductory astronomy labs and first-year writing there for over 30 years (not necessarily all at the same time). He was educated at Biglerville High School, the University of Virginia, and the University of Iowa. He lives in Gettysburg.

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