Skywatch Line for Friday, July 14, through Sunday, July 16, 2023

This is Dudley Observatory’s Skywatch Line for Friday, July 14, through Sunday, July 16, written by Sam Salem.

On Friday, Sun rises at 5:29am and sets at 8:32pm; Moon rises at 2:24am and sets at 6:32pm.

Start looking for Mercury just above the west-northwest horizon about 20 minutes after sunset. Mercury is very deep in the glow of sunset, but a little less so each day. It’s lower right of Venus. Venus moves toward Mercury by about a degree a day.

Venus, at magnitude –4.7, dominates the low west in twilight. It’s dropping sunward faster now day by day. It sets while twilight is still in progress. Venus is a tiny 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 42 arcseconds in diameter, while waning to 19% sunlit on Friday. It will continue to swell in diameter and thin in phase as it drops lower. It will be lost from sight later in the month. Even good binoculars are enough to show Venus’ tiny crescent. Try during twilight before the sky becomes too dark and Venus’s glare too spready. You can also try during late afternoon in a clear blue sky while it’s still high.

Mars, at magnitude 1.7, glows weakly to Venus’ upper left low in the west at dusk. They’re beginning to draw apart. On Friday, Mars and Venus are separated by 6 degrees.

Jupiter, at magnitude –2.3 in the constellation of Aries, rises around 2am in the east-northeast. By the beginning of dawn, it shines high in the east.

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. Fomalhaut, the 1st-magnitude star in the constellation of Piscis Austrinus, sits about two fists below Saturn.

Albireo, also known as Beta Cygni, is the second-brightest star in the constellation of Cygnus the Swan. It doesn’t particularly stand out. But viewing this star through a small telescope resolves into a striking double, with one component a gold star and the other a dimmer blue star close by. From our perspective, the two stars appear close in the sky. But astronomers don’t believe they’re gravitationally bound to each other. The color contrast between the two is so striking that Albireo is considered the most beautiful double star in the heavens. It’s easy to find Albireo if you can locate Cygnus the Swan. Cygnus has an easy-to-recognize shape, that of a cross. The constellation is also known as the Northern Cross. The brightest star in Cygnus, Deneb, marks the head of the Cross, or the Tail of the Swan. Albireo marks the base of the Cross, or the Head of the Swan.