by Geoff Chester, USNO Public Affairs | 07 June 2023 Messier 31 the Great Hercules Cluster, imaged 2022 April 30 from Alexandria, Virginia with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor and a ZWO ASI183MC CMOS color imager The Moon wanes in the morning sky this week, gradually climbing northward through the rising autumnal constellations. Last Quarter occurs on the 10th at 3:31 pm Eastern Daylight Time. Look for Luna near the yellow glow of Saturn on the mornings of the 9th and 10th. She closes in on the much brighter planet Jupiter in the gathering morning twilight by the week’s end. As the Moon slips into the morning sky, the June campaign for the citizen science program Globe at Night gets underway on the evening of the 9th and runs through the 18th. Since we are now experiencing the shortest nights of the year, you don’t have much time to count stars for the program, so it is important to secure as many observations as possible. Evening astronomical twilight doesn’t end until after 10:30 pm here in Washington, so prepare for a late night to make your contribution. You have two constellations to choose from this month: Boötes the Herdsman or Hercules the Strongman. Boötes is the better choice for the suburban skywatcher, while Hercules is better for viewers in dark locations. The Herdsman’s brightest star is easily seen on the meridian at the end of evening twilight. It is the brightest star in the northern sky, and the fifth-brightest of all the stars. It is the base of a large, kite-shaped asterism made up of a second-magnitude star, Izar, and a group of third-magnitude stars that lie straight overhead at 10:30 pm. Hercules is a large constellation that occupies the area between Arcturus and the bright star Vega, now rising in the northeast. Its central region is marked by a trapezoid of second- and third-magnitude stars that is often called “The Keystone”. To make a report for Globe at Night, locate either constellation, then compare your view with the magnitude charts found on the Globe at Night web app. Both Boötes and Hercules host some interesting sights for owners of small to medium-aperture telescopes. Izar, the second-brightest star in the Herdsman, is a colorful double star with blue and yellow-hued component that can be resolved in a three-inch telescope. It was dubbed “Pulcherrima” by the great 19th Century observer Wilhelm Struve, who felt that it was the most beautiful in the sky. If you’re away from city lights, use binoculars to track down Messier 3, a globular star cluster about 12 degrees northwest of Arcturus. It will be a round fuzzy patch of light in binoculars, but a 4-inch or larger telescope will reveal its true nature as a concentrated mass of thousands of faint stars. An even more spectacular globular cluster, Messier 13, lies in the constellation of Hercules in the central “Keystone” asterism. Once again, use binoculars to locate the fuzzy glow just below the Keystone’s northwestern corner. Once again, a good 4-inch telescope will begin to resolve it into a swarm of faint stars, and each increase in aperture will bring out more detail. In my 14.5-inch reflector telescope it is a magnificent sight, filling the field of view with thousands of stars that blend together as they become more concentrated toward the cluster’s center. There are some 300,000 stars in the cluster, which lies about 22,500 light-years away. It is the brightest of the 100 or so similar clusters visible from our latitude. Globular clusters are made up of some of the oldest stars known in the universe; M13 is thought to have stars over 11 billion years old! It is close to the “apex of the Sun’s way”, the point in space toward which the Sun (and by extension us) is moving. This prompted the novelist Kurt Vonnegut, Jr. to write, "Every passing hour brings the Solar System forty-three thousand miles closer to Globular Cluster M13 in Hercules—and still there are some misfits who insist that there is no such thing as progress." Venus continues to chase Mars through the dim constellation of Cancer, the Crab. However, her eastward motion against the stars is beginning to slow in pace, so she only gains about two degrees on the red planet. By the end of the week, look for Venus to approach the Beehive star cluster. She crosses the cluster’s northern edge on the evening of the 13th. Mars seems to keep the pursuit by Venus at bay during the week. By week’s end the two planets are just over six degrees apart. Over the next few weeks Venus will close to about three degrees of the red planet, but she won’t quite catch him. As June turns to July she will begin the long plunge toward the Sun. Saturn is well-placed for early risers, glowing with a pale yellow tint in the southeast as morning twilight begins. The only comparably bright object near him is the star Fomalhaut, some 20 degrees below the ringed planet. You will find the brighter glow of Jupiter low in the east about 45 minutes before sunrise. The giant planet will continue to climb in the morning sky, and by the end of the month he should be easy to spot in a dark morning sky.