Skywatch Line for Friday, September 1, through Sunday, September 3, 2023

This is Dudley Observatory’s Skywatch Line for Friday, September 1, through Sunday, September 3, written by Sam Salem.

On Friday, Sun rises at 6:20am and sets at 7:30pm; Moon sets at 8:04am and rises at 8:36pm. On Sunday night, use your telescope to explore the Moon in its interesting waning gibbous phase. Lunar landforms near the terminator cast their shadows in the opposite direction from when the Moon is a thick waxing crescent seen in early evening.

On Sunday, watch Jupiter shining right nearby the Moon. Jupiter, at magnitude –2.6 in the constellation of Aries, rises about an hour after full dark. Watch for it to come up low in the east-northeast. Jupiter shines highest in the south just before the beginning of dawn. Jupiter’s four bright Galilean moons are very roughly the size of our own Moon, but at 1,800 times the distance, they appear in a telescope as hardly more than pinpoints. Jupiter’s Great Red Spot should transit the planet’s central meridian on Sunday night around 1am.

Venus, about magnitude –4.6, is fast emerging low in brightening dawn. Look for it above the horizon due east. It gets higher and easier every day. Even low magnification shows that Venus is again a thin crescent. The crescent will get thicker and smaller in the coming weeks as it climbs higher in the dawn.

Saturn, at magnitude +0.4 in dim constellation of Aquarius, rises at sunset. It’s was at opposition on August 26th. In late twilight you’ll find Saturn glowing as the brightest thing low in the east-southeast. It’s at a good height for telescopic observing by 11pm. By that time, Fomalhaut is twinkling two fists below the planet. Saturn is at its highest in the south around 1am.

Uranus, magnitude 5.7 in the constellation of Aries, is high by midnight, 8 degrees east of Jupiter.

Neptune, magnitude 7.8 at the Aquarius-Pisces border, is high by late evening, 23 degrees east of Saturn.

The two brightest stars of September evenings are Vega, high overhead, and Arcturus, in the west. Both stars are magnitude 0. Draw a line from Vega down to Arcturus. A third of the way down you cross the dim Keystone of Hercules. Two thirds of the way you cross the dim semicircle of Corona Borealis displaying its one modestly bright star, Alphecca. The star is sometimes called Gemma, which means the gem of the crown. Like the star Algol in the constellation of Perseus, Alphecca is an eclipsing binary star, with an orbital period of about 17.4 days. Unlike Algol, as one star passes in front of the other in Alphecca system, the star’s variation in brightness is barely perceptible. Alphecca is derived from Arabic phrase “al-nair al-fakka”, which means the bright star of the broken ring.