This is the Dudley Observatory Skywatch Line for Wednesday, June 10th, and Thursday, June 11th, written by Louis Suarato.
Wednesday, the 77% illuminated, waning gibbous Moon sets at 10:02 a.m., before rising again at 44 minutes past midnight on Thursday. Mercury remains in the sky until 10:08 p.m., between the Gemini twins. Look for Mercury low over the west-northwestern horizon after sunset. Jupiter rises at 10:48 p.m., followed by Saturn 16 minutes later. The gas giants will be between the constellations Capricornus and Sagittarius. Mars joins Jupiter and Saturn at 1:24 a.m., 40 minutes past moonrise. Friday, the Moon and Mars will rise side by side, separated by 10 degrees. The pre-dawn sky demonstrates how the plane of the ecliptic, the planets path around the Sun, flattens around the time of the solstice. Mars, Saturn and Jupiter span 61 degrees, but their difference in altitude is only 3 degrees.
Astronomical Twilight, when the Sun is between 12 and 18 degrees below the horizon, and most stars can be seen, occurs at 10:48 p.m., Wednesday. If you look up at the sky at that time, you can see Cygnus, the Swan, taking off from the northeastern horizon. Cygnus’ brightest star is Deneb, or Alpha Cygni, a first magnitude white supergiant star, at the tail of the Swan. Deneb is one of the largest, and most luminous A-Class stars. Deneb is also a component of the asterisms known as the Summer Triangle, and the head of the Northern Cross. To the east of Deneb, at the center of the Cross, and between the Swan’s wings are four open star clusters. M29, or NGC 7092, contains about 30 stars, the brightest of which are 7th magnitude. NGC 6910, The Rocking Horse Cluster, has 16 stars, the brightest being 2 gold stars. Farther east is a younger open star cluster, IC 4996. The stars in this cluster have been estimated to be between 8 and 10 million years. The fourth cluster is NGC 6871. This small cluster contains about 50 stars, mostly blue and white, estimated to be about 9 million years, and 5,135 light-years away. At the very tip of the Swan is the star Albireo. Albireo is a gem of a double star comprised of gold and blue stars. Use a low power telescope to split and resolve these stars.