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The Sky this Week, October 25-31

“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.  The next public show is Thursday, November 3, at 12:00 Noon.

If you go outside this week after 10:30 p.m., you’ll find a striking grouping of three bright objects: the stars Capella and Aldebaran and the planet Mars (see image). Expect Mars to be the brightest, followed by Capella and then Aldebaran. Above Aldebaran, look for a little cluster of stars; these are the Pleiades. Mentioned by Homer and often called the “Seven Sisters,” this tiny cluster of stars contains not seven but about 500 members. It’s a true cluster of stars in space about 400 light years from our solar system. An observer with average eyesight can see six with the unaided eye in a fairly dark sky. Two or three more may be glimpsed under excellent conditions. Good binoculars will reveal dozens. In December 1579, before the invention of the telescope, the German astronomer Michael Moestlin mapped the Pleiades. He cataloged 11 stars—all, we now know, in their correct positions. Moelstin probably used only a “radius astronomicus,” an ancestor of the sextant. He could not have known that a few decades later, an optical instrument would be invented that would confirm what he could only have seen as the faintest of glimmers or that a few centuries after his death, humankind would launch such an instrument into space to view the Pleiades and much more free from the murk of earth’s atmosphere. Nevertheless, his correct and careful records give us some idea of how dark a sixteenth-century European sky must have been.

930 oct 25

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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