This is the Dudley Observatory Skywatch Line for Wednesday, May 8th, and Thursday, May 9th, written by Louis Suarato.
The 15% illuminated, waxing crescent Moon rises at 8:30 a.m. in the constellation Gemini, and sets three minutes after midnight. Thursday night, look to the Moon’s upper left for the Beehive Cluster, the 44th object in Messier’s catalogue. Mars leads the crescent Moon across the sky until setting at 11:11p.m. in the northwest. Jupiter rises at 10:49 p.m. in Ophiuchus. A telescopic view of Jupiter will show the four Galilean moons throughout the night. Ganymede and Callisto will be on one side, and Europa and Io on the other side. Saturn begins to cross the sky at 41 minutes past midnight within Sagittarius.
An open star cluster is a group of about a thousand stars that were formed out of the same molecular cloud, and are approximately the same age and chemical composition. There are more than 1,100 open star clusters that have been discovered in the Milky Way Galaxy. Messier’s catalogue contains 26 open star clusters. Unlike globular star clusters, open cluster stars are loosely bound by the same gravitational forces, These forces can be broken by encounters with other clusters, and stars can migrate away from other member stars. Most open clusters are found away from the galactic center, where strong tidal forces can pull apart the loosely connected stars. Since older stars are dispersed from open clusters most open clusters are populated by young, hot blue stars. The brightest open star clusters in our sky, such as the Pleiades and Hyades, can be seen with the naked eye. Others, such as the Beehive and Double Cluster, can be seen through binoculars. The Hyades, in the constellation Taurus, is the closest open star cluster to our solar system. The stars from the Hyades are about 153 light-years away.