“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. Public shows have concluded for the academic year, but we are still accepting field trip requests for the summer!
The moon is new this week on the 19th, which means you won’t see it in the night sky. Moonless nights are best for stargazing. If you look high in the east after it’s completely dark, you’ll find the Big Dipper. This familiar star group is not officially a constellation; the whole constellation is Ursa Major or the Great Bear. Because it’s well-known, it is a good starting point for locating other things in the sky. This week try extending the curve of the dipper’s handle in your imagination. You will find it points toward a bright reddish star—Arcturus. Congratulations, you have “followed the arc to Arcturus.” Arcturus is the fourth brightest star in the sky, and it is noted for its high “proper motion,” or movement relative to other stars. This is not to be confused with the motions of the sky caused by the rotation or revolution of the earth, which does not change the positions of stars relative to each other. Proper motion will actually distort the shapes of constellations over long periods of time. You won’t notice Arcturus moving over your lifetime, but in about a half million years, it will have moved so far from us that it will no longer be visible without a telescope.
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.