Last updateTue, 18 Sep 2018 1pm


31 Aug 2017
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Our morning twilight all-sky chart for September, viewable below, shows the changes in positions of the naked-eye planets and the stars of first-magnitude or brighter, less than an hour before sunrise. Changes are caused by the motion of the Earth and the other planets in their orbits. Stars will appear to drift from east to west across the sky as weeks pass, thanks to the revolution of Earth around the sun. Venus now dominates the predawn sky, but is getting a little lower each morning, because it is heading toward the far side of the sun, where it will arrive in January 2018. Annually in September and October, the huge Winter Hexagon—in clockwise order from its brightest member, Sirius, Procyon, Pollux and Castor, Capella, Aldebaran and Rigel, with Betelgeuse inside—is well-placed high in the sky before dawn. The flashing blue-white Dog Star Sirius is its most prominent and southernmost member.…
28 Jul 2017
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The summer of 2017 marks the 54th anniversary of my first successful expedition to observe a total solar eclipse. The date was July 20, 1963, when our carload of astronomy graduate students from the University of Michigan made the long drive from Ann Arbor to the path of totality in Quebec. Cumulus clouds parted—and we had a spectacular view. When it came to astronomy, I was hooked. I hope some of you have a chance to make the journey to the August eclipse’s path of totality. This event is part of the Saros series—same as the eclipse I saw in 1963. These eclipses are spaced at intervals of 18 years plus about 11 1/3 days, and after three Saros intervals—called an Exeligmos—a solar eclipse very much like the one in 1963 happens again, within a similar track through our region of the world, only farther south. Instead of Alaska through…
30 Jun 2017
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July finds bright Jupiter in the south-southwestern sky at dusk, and Saturn in the southeast, closing to 65 degrees apart by month’s end. Before dawn, Venus gleams in the east, against the attractive background of Taurus the Bull, with its two prominent star clusters and bright reddish star. On some dates, the moon forms attractive pairings with four of the five naked-eye planets, and four of the five bright zodiacal stars. In July’s evening twilight, bright Jupiter attracts attention in the southwest, with bluish Spica nearby to its left, and golden Arcturus high above them. Yellowish Saturn glows steadily in the southeast to south-southeast, in contrast to the vigorously twinkling reddish star Antares, heart of the Scorpion, to its right. The star reaches south in mid-twilight near month’s end. The Summer Triangle, topped by its brightest star, blue-white Vega, ascends in the eastern sky. The Triangle’s other members are Altair,…