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The Sky this Week, August 15-22

“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, schedule of free public shows is coming soon.

We just passed the full moon phase on the night of August 11-12, and now you may notice that the moon is gone from the evening sky. There are a couple of useful rules of thumb to remember about the moon cycle. First, when the moon is full it is opposite the sun from our point of view. Therefore it rises around sunset and sets around sunrise. This is only true at full moon, and the actual timing varies a bit; but it’s a good approximation. For the next rule of thumb, the moon rises about 50 minutes later each night. So now (Tuesday, August 16) the moon will rise just before 11:00 p.m., and it will rise later each night as the phase wanes.

Before the moon comes up, look at the stars in the northern sky. It’s a good place to begin finding your way around. As long as you’re in the earth’s northern hemisphere, you will always find the Polaris (the North Star) due north at a height above the horizon equal to your latitude. For us, that’s 40 degrees, with the horizon being zero and the zenith 90. Contrary to popular misconception, Polaris is not especially bright; it’s only the 48th brightest star. What’s special is its location very near the celestial north pole. This means that as the earth rotates, all the other stars seem to revolve around it each night. No matter what time of night or year, however, you will always find the two constellations Cassiopeia and Ursa Major (which contains the “Big Dipper”) opposite one another.

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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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  • Looking forward to list of public shows. Have been looking up since I was a kid.

    Also suggest subscribing to NASA’s “Spot the Station” texts. Always beautiful to see it move across the night sky!

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