The Sky this Week, September 13-19

“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 Fall 2022 is now live, and the schedule of free public shows has been posted.

Let’s talk today about the most distant object you can see without optical aid, the Andromeda Galaxy. You’ll need a moonless night far from artificial lights to see it. If you can easily see the Milky Way, then you should be able to see the Andromeda Galaxy as a faint, fuzzy spot. The accompanying illustration will tell you where to look. If you can’t see it with the unaided eye, a good pair of binoculars should bring it out. Look for a fuzzy oval in the spot shown on the map. That fuzzy spot is the combined light of about a trillion stars at a distance from us of 2.5 million light years. (One light year is 5.9 trillion miles.) As distant as that may seem, the Andromeda Galaxy is a neighbor of ours, a member of our Local Group of galaxies. The Local Group itself is a part of the Virgo Supercluster of galaxies, whose center lies 65 million light years away. The Virgo supercluster in turn is only one of the millions of such groups in the observable universe.

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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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