Skywatch Line for Friday, July 21, through Sunday, July 23, 2023
This is Dudley Observatory’s Skywatch Line for Friday, July 21, through Sunday, July 23, written by Sam Salem.
On Friday, Sun rises at 5:36am and sets at 8:27pm; Moon rises at 9:08am and sets at 10:44pm. In late twilight on Friday, look for Denebola, Beta Leonis, about a fist at arm’s length above the Moon. Denebola is Leo’s tail tip.
On Saturday, spot the crescent Moon in the west-southwest, about 30 minutes after sunset. Look for Venus about three fists at arm’s length to its lower right. Fainter Mercury and Mars form a straight diagonal line a little way above Venus. The line is about fist and a half long, from lower right to upper left.
On Sunday evening, explore the thick waxing crescent phase using a telescope to explore the Moon’s terminator While being there, explore the 3rd-magnitude Gamma Virginis, or Porrima, above or upper right of the Moon by a couple degrees. It is a fine close double star. Its components are 3.3 arcseconds apart this year, oriented almost north-south. They’re both magnitude 3.5.
Mercury is 11° from Venus on Friday. Mercury is deep in the glow of sunset to the lower right of brighter Venus. Start looking for them about 20 minutes after sunset. Binoculars help. Mercury fades to magnitude –0.3.
Venus, at magnitude –4.6, is the first point of light you’ll see low in the west as twilight fades. It sets during twilight, sooner every day. Get your telescope on Venus during late afternoon in a clear blue sky while it’s still high. Venus is a tiny, thin white crescent, enlarging and thinning and as it swings closer to Earth and closer to our line of sight to the Sun. It expands to 46 arcseconds in diameter while waning to 15% sunlit on Friday. It will continue to swell and thin in phase as it drops toward its conjunction with the Sun.
Mars, at magnitude +1.8, glows weakly upper left of Venus as twilight deepens. They’re 9½° apart on Friday. Between them is sparkly Regulus, magnitude +1.4, noticeably brighter than Mars. In a telescope Mars is a tiny blob 4 arcseconds in diameter.
Jupiter, at magnitude –2.3 in the constellation of Aries, rises around 1am in the east-northeast. By the beginning of dawn, it shines high toward the east-southeast.
Saturn, at magnitude +0.8 in dim constellation of Aquarius, rises around 11pm. It’s at its highest in the south and sharpest and steadiest in a telescope just before dawn begins. The 1st-magnitude star Fomalhaut sits about two fists below Saturn.
Uranus, at magnitude 5.8 in the constellation of Aries, is well up in the east by the beginning of dawn. It’s about 11° lower left of Jupiter.
Neptune, at magnitude 7.9 at the Aquarius-Pisces border, is highest in the southeast before dawn begins, about 20° east of Saturn.