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Skywatch

Mon May 16, 2016 ARCTURUS THE INTEROLOPER

Halfway up in the eastern sky this evening there is a star that doesn’t belong here – an interloper. It’s Arcturus, the fourth brightest star in our night sky, and it’s a visitor from beyond the galactic disc. Arcturus is an old red giant, and while most of the stars you see up there are moving along with our sun, traveling in nearly circular orbits about the hub of our Milky Way galaxy, Arcturus moves at a sharp angle to all the others. Our sun and planets are embedded within the Milky Way’s disc, and our orbit carries us along in the plane of the disc as we revolve. But Arcturus is plunging along an elliptical path through the disc from up above. Tonight, it’s a mere 37 light years away, that’s a bit more than 200 trillion miles, but in a half million years or so it will have shot down below us, and its ever increasing distance will make it too dim to see without a telescope. So enjoy viewing Arcturus while it’s still in the neighborhood!