Star light, star of the first magnitude

The Sky This Week, October 31-November 6

“The Sky This Week” appears regularly. 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. We are accepting field trip requests for the 23-24 academic year. The fall schedule of public shows is available here! Illustrations created with Stellarium.

Since the time of the ancient Greek astronomer Hipparchus, astronomers have talked about the brightness of stars in “magnitudes,” with a “first magnitude” star being very bright and a “sixth magnitude” star being barely visible. Over the centuries, this notation has evolved into a mathematically precise system. Sirius, the brightest star in our sky, has an apparent magnitude of -1.4, for example. But still, a “first magnitude” star is a bright star. Well, the southernmost first-magnitude star that you can see from Gettysburg, PA, is visible right now. Look south at about 9:00 p.m. EDT to find this star 20 degrees above the horizon. Don’t confuse it with the planet Saturn, above and to its right. Fomalhaut is the brightest star in a faint constellation, Piscis Austrinus (the Southern Fish). Fomalhaut lies 25 light-years from our solar system and has been caught in the act of developing a planetary system of its own. Based on infrared emissions from the star, astronomers had long suspected that a ring or disk of debris might surround Fomalhaut. This disk was first revealed directly in 1983. Now the James Webb Space Telescope, which specializes in the infrared end of the spectrum, has imaged this debris disk in the greatest detail yet. Just imagine what you’re really looking at as you gaze at lonely Fomalhaut in the southern sky.

JWST image credit: NASA, ESA, CSA, A. Gáspár (University of Arizona). Image processing: A. Pagan (STScI)

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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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