Skywatch Line for Friday, May 10, through Sunday, May 12, written by Sam Salem

This is Dudley Observatory’s Skywatch Line for Friday, May 10, through Sunday, May 12, written by Sam Salem.

On Friday, Sun rises at 5:37am and sets at 8:07pm; Moon rises at 7:03am and sets at 11:38pm.

On Friday evening, the waxing crescent Moon, glowing with earthshine, will lie between two bright stars. The golden star is Capella in the constellation Auriga the Charioteer, and the bright red supergiant star Betelgeuse, the brightest star in Orion the Hunter. You can follow them until almost midnight.

On Sunday evening, the waxing crescent Moon will shine near Pollux and Castor, the twin stars of Gemini. Pollux is a bit brighter and it’s a golden star, while Castor is a white light. They’ll rise before sunset and travel across the sky’s dome before setting near midnight.

Mars and Saturn, both about magnitude +1.2, rise around the beginning of dawn. Look low above the east-southeast horizon about 60 minutes before sunrise. Saturn is the easier one. Mars is off to Saturn’s lower left. They are 21° apart on Saturday Morning.

Three zero-magnitude stars shine after dark in May: Arcturus high in the southeast, Vega much lower in the northeast, and Capella in the northwest. They appear so bright because each is at least 60 times as luminous as the Sun, and because they’re all relatively nearby: 37, 25, and 42 light-years from us, respectively. On Friday evening, Vega and Capella stand at the same height above the horizon shortly after dark.

Arcturus is a red giant star. It’s the 4th-brightest star in the sky and the brightest one in the northern half of the sky. Look for it on spring evenings in the Northern Hemisphere by arcing to Arcturus from the Big Dipper’s handle. Arcturus is the alpha star of a cone-shaped constellation called Boötes the Herdsman. It’s far enough north on the sky’s dome that, for Northern Hemisphere observers, it’s visible during some part of the night throughout most of the year. There’s an easy mnemonic for identifying this brilliant orange star: follow the arc to Arcturus and then speed on to Spica.

First, locate the Big Dipper in the northern sky, the handle of the Big Dipper is a curve or arc. Extend this curve past the end of the Big Dipper’s handle, and you’ll reach Arcturus.

Unlike most of the bright stars in the nighttime sky, Arcturus has no bright neighbors. It commands the sky in the springtime and reigns the heavens until the Summer Triangle takes over the eastern sky.

This is the time of year when Leo the Lion starts walking downward toward the west, on his way to departing into the sunset in early summer. Right after dark, spot the brightest star high in the west-southwest. That’s Regulus, his forefoot. Regulus is also the bottom of the Sickle of Leo: a backward question mark about a fist and a half tall that outlines the lion’s leading foot, chest, and mane.