by Geoff Chester, USNO Public Affairs | 04 June 2024 Messier 13, the Great Hercules Cluster, imaged 2024 May 25 from Mollusk, Virginia with a ZWO Seestar S50 Smart Telescope The Moon returns to the evening sky this week, passing through the last of winter’s stars and ending the week near the bright star Regulus in Leo, the Lion. New Moon occurs on the 6th at 8:38 am Eastern Daylight Time. Look for Luna’s slender crescent just below the Twin Stars of Gemini, Castor and Pollux, on the evening of the 8th. Keep an eye out for “Earthshine” illuminating the part of the Moon’s disc that’s not lit by the Sun. You should be able to see this ghostly glow for the next several nights. On the 9th, use binoculars to follow a line from the star Pollux through the Moon to a scattering of stars known as the Praesepe or The Beehive. This is one of the nearest galactic star clusters to the solar system, lying at a distance of 590 light years. Under dark skies it is visible as a hazy patch to the naked eye, and it has been recognized since antiquity. The Greek astronomer/philosopher Aratus mentioned the Beehive as an indicator of approaching storms; if the cluster wasn’t visible on an otherwise clear night, bad weather was approaching. Binoculars will show a widely scattered grouping of several dozen stars. A wide-field telescope will increase that number to about 100. The total number of stars associated with it is around 1000, making it one of the richest nearby star clusters. The season’s brightest star, Arcturus, now crosses the meridian at around 10:00 pm. For most of the spring, Arcturus was the sole bright beacon in the evening sky, but now, as it drifts westward from the meridian, a bright blue-tinted star is becoming prominent in the east. This is Vega, the brightest star in the diminutive constellation of Lyra, the Harp. Slightly dimmer than Arcturus, Vega is still the fifth-brightest star in the sky, and it forms one apex of the asterism known as the Summer Triangle, which will dominate the overnight hours throughout the next few months. Vega is bright due to its relative proximity to us, some 25 light years away. It shines with about 40 times the luminosity of the Sun, and was the first star other than the Sun to be photographed and have its spectrum measured. It was the northern “pole star” some 12,000 years ago, and it will once again assume that role in another 13,000 years thanks to precession of the Earth’s rotational poles. About one-third of the way from Vega to Arcturus is the ancient constellation of Hercules, one of the most popular figures in Greek mythology. I have often wondered why this character, known for his twelve heroic labors, didn’t get a bright constellation like Orion, who was something of a brash, hot-tempered individual. Either way, the stars of Hercules are fairly dim, but the brightest form a distinctive four star asterism known as the Keystone. Use binoculars to scan the western side of the Keystone and you will notice a round, fuzzy spot. This is another star cluster, but one that is entirely different from the Beehive. Messier 13, the Great Hercules Cluster, is a vast remote cluster of nearly half a million stars known as a globular cluster. These clusters have long, looping orbits that carry them through the plane of the galaxy, stripping out the gas and dust that forms new stars. The stars in these clusters are some of the oldest in the universe, well over 10 billion years old. The Hercules cluster is a splendid sight in a modest telescope, with each increase in aperture revealing more stars that become more concentrated toward the center. At about 22,000 light years it is the nearest such cluster in the northern sky and is a favorite sight at summer star parties. The pre-dawn sky is where you will find the brighter planets this week. The first to rise is Saturn, which crests the horizon at around 1:30 am. Next up is ruddy Mars, which rises at around 3:00 am. By 5:00 am they are prominent in the southeastern sky, but they are competing with the increasing twilight.