Skywatch Line for Friday, May 24, through Sunday, May 26, written by Sam Salem
This is Dudley Observatory’s Skywatch Line for Friday, May 24, through Sunday, May 26, written by Sam Salem.
On Friday, Sun rises at 5:24am and sets at 8:21pm; Moon sets at 5:39am and rises at 10:08pm.
On Sunday, the waning gibbous Moon rises around midnight. Once it’s well up, cover it with your fingertip to help reveal that it’s in the middle of the Sagittarius Teapot.
Look for Mercury, Mars, and Saturn low during dawn. Saturn is the easiest, well up in the east-southeast as dawn begins. It’s magnitude 1.2, and nothing else that bright is anywhere near it. Far lower left of Saturn is Mars, about the same brightness but harder to see in the brightening dawn. They widen apart to 30°, or about three fists at arm’s length, on Saturday. Mercury is far lower left of Mars. Those two planets are 25° apart on Saturday. Use binoculars to try for Mercury through bright twilight a half hour before sunrise. This is about your last chance at Mercury this apparition.
Vega is the brightest star shining in the east-northeast after dark. Look lower left of it, by about two fists at arm’s length, for less bright Deneb. Those stars are two thirds of the Summer Triangle. With summer still four weeks away, the third Summer Triangle star, Altair, stays below the eastern horizon until somewhat after dark. Watch for it to clear the horizon three or four fists at arm’s length to Vega’s lower right.
Look for Vega’s faint little constellation Lyra, the Lyre, hanging down from it with its bottom canted to the right. The most familiar part of Lyra consists of a little equilateral triangle, where Vega lies in one corner, with a larger parallelogram attached to its bottom corner. The whole constellation is 7½° long, about four finger-widths at arm’s length. The bottom two stars of the parallelogram, Beta and Gamma Lyrae, are the two brightest stars of the pattern after Vega. Gamma is the one farthest from Vega. Most of the time those two are almost indistinguishable in brightness. Gamma is visual magnitude 3.25 and Beta is 3.4. Beta is a famous eclipsing variable, one of the first discovered. Look up at these two at different times, and sooner or later you will catch Beta very obviously dimmer than Gamma, at its minimum brightness of mag 4.3. More often you’re likely to catch it somewhere in between, when the difference is apparent but not so striking.
Capella sets low in the northwest not very long after dark. That leaves Vega and Arcturus as the brightest stars in the evening sky. Vega shines in the east-northeast. Arcturus is very high toward the south. Right after full dark and before the Moon rises, look a third of the way from Arcturus to Vega for semicircular Corona Borealis, with 2nd-magnitude Alphecca as its one moderately bright star. Two thirds of the way from Arcturus to Vega is the dim Keystone of Hercules, now lying almost level. Use binoculars or a telescope to examine the Keystone’s top edge. A third of the way from its left end to the right is 6th-magnitude M13, one of Hercules’s two great globular star clusters. In binoculars it’s a tiny glowing cotton ball. M13 is located 22,000 light-years away far above the plane of the Milky Way. It consists of several hundred thousand stars in a swarm about 140 light-years wide.