Skywatch Line for Friday, May 11 through Sunday, May 13, 2018

This is Dudley Observatory’s Skywatch Line for Friday, May 11 through Sunday, May 13, written by Sam Salem.

On Friday, the Sun rises at 5:37am and sets at 8:08pm; the waning crescent Moon rises at 3:53am and sets at 3:49pm.

Venus, at magnitude –3.9, and Jupiter, at magnitude –2.5, hang roughly 10 degrees above the horizon a little before 10pm. Jupiter, in constellation Libra, sits in the southeast, and Venus is in the west-northwest, separated by 150 degrees of azimuth, or horizontal angle. Jupiter reached opposition on Wednesday. This weekend Jupiter climbs to the meridian around 1am. Your chance to view the Great Red Spot this weekend will be when it’s on Jupiter’s central meridian on Sunday morning at 12:37am.

Mars, at magnitudes –0.6, rises a little after 1:00am. Saturn, at magnitude 0.3, rises a little before midnight. They’re on opposite sides of Sagittarius, with Mars on the lower left. Saturn is above the Teapot asterism in Sagittarius. By early dawn they’re higher in the south.

Look for constellation Corona Borealis, the Northern Crown, between the brilliant stars Arcturus, in the constellation Bootes the Herdsman, and Vega, in the constellation Lyra the Harp. This constellation is very noticeable if you have a dark sky. Corona Borealis is an almost-perfect semi-circle of stars. At nightfall and early evening, Arcturus is fairly high in the east to northeast, noticeable for its brightness and yellow-orange color. Bright and blue-white color Vega will be rather low in northeast. The Northern Crown is more or less between these two bright stars. The brightest star in Corona Borealis is Alphecca, also known as Gemma, sometimes called the Pearl of the Crown. The name Alphecca is Arabic, originated with a description of Corona Borealis as the “broken one,” in reference that these stars appear in a semi-circle, rather than a full circle. Alphecca is a blue-white star with an intrinsic luminosity some 60 times that of our Sun. It’s located about 75 light-years from Earth.

Vega and Arcturus can also guide you to the Keystone, a pattern of four stars in the constellation Hercules. Arcturus is found quite high in the southeast sky at nightfall and evening. By late evening, Arcturus will have moved over to the southern sky. The Keystone is found about one-third the way from Vega to Arcturus. Use the Keystone pattern to locate the Great Cluster in Hercules, or M13. Hercules Globular Cluster is a globular cluster of about 300,000 stars in the constellation of Hercules. The Keystone and the Hercules cluster swing high overhead after midnight, and are found in the western sky before dawn. M13 was discovered by Edmond Halley in 1714, and cataloged by Charles Messier in 1764. Sharp-eyed people can see the Hercules cluster with the unaided eye in a dark, transparent sky. Through binoculars, this cluster looks like a dim and somewhat hazy star. Telescope resolves the details of the cluster into a great big, globe-shaped stellar city populated with hundreds of thousands of stars.

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