Straight overhead in the early evenings of July is the constellation Hercules. Unfortunately, in July, “early evenings” means after 10:30 p.m.
Legends about his exploits go back farther than history records. Even before the ancient Greeks, he was seen as the “kneeling man” in many cultures. As he kneels, he places his left foot on the head of the giant dragon Draco, who stretches below him in the northern sky.
He represented for the ancient Greeks and Romans the highest ideals of bravery and headstrong heroism.
Hercules has the privilege of containing the most beautiful astronomical object in the northern sky, the Great Globular Star Cluster.
To find it, you must first find the constellation. After evening twilight, look high in the eastern sky for the very bright star Vega. West of Vega, almost straight overhead, is a large, rough square of stars called the Keystone. It makes up the trunk of Hercules’ body. His upraised arms stretch south and his legs are to the north.
Find the two stars on the west side of the Keystone. About a third of the way up from the north-most star, you will see a small, fuzzy, round patch in binoculars, marked as M13 on the star chart.
It must have been easily visible to the ancients without optical aid because even with today’s light pollution, it is visible to the naked eye from dark, rural sites.
You are looking at more than a quarter of a million stars in one telescope field. M13 is an explosion of starlight so dense that it is difficult to resolve the stars into individual points of light except in a large telescope.
Globular clusters like M13 are composed of very old stars that are very close together. At about 25,000 light years away, M13 is about as far away as an astronomical object can get and still be in our Milky Way galaxy. “Globulars” are clusters of stars that huddle around the dense galactic core but outside the disk of the galaxy, out in the galactic suburbs, you might say. M13 is perhaps 100 light years, or 600 trillion miles, in diameter.
Words fail me here. M13 is a tremendous sight in a telescope. It looks like a globe of stars, dense with countless points of light at the center and slowly becoming sparser as you move outward. It looks like a giant swarm of fireflies or a pile of diamond dust—so many stars that it is impossible to count them.
Imagine what it would be like to live on a planet circling around one of those stars. The nighttime sky would be glorious, so filled with stars that it might even seem like daytime. Stargazers would probably never guess that he was part of a larger galaxy in a universe of many galaxies. They could never see past their own stellar neighborhood.
Its home constellation Hercules had the misfortune of being born out of the dalliance of Zeus, the king of the gods, and a mortal woman named Alcmene.
Zeus’ wife, Hera, was extremely jealous of Zeus’ many mortal lovers, but she couldn’t do much to get revenge against her more powerful husband.
So she took it out on the mortals. Hera had had a grudge against Hercules ever since he was born, and Hercules had to face her considerable wrath for most of his life.
Like the other gods, Hercules had a considerable temper and a great appetite for adventure.
The night sky is littered with the carcasses of the great beasts that Hercules killed during his eventful, heroic life.
His bloody presence is felt all over the sky. Among his famous Twelve Labors, he killed the Lernean Hydra, visible as a long string of stars low in the southern spring sky. He also killed the Nemean Lion, which is said to be the constellation Leo, now setting in the western sky. Just below Leo in the southern sky is Cancer, the giant crab, slain by Hercules as he battled the Hydra.
The Crab, the Lion and the Hydra were the nasty household pets of Hera, wife of Zeus and queen of the gods. She sent them to bedevil humanity in general and Hercules in specific. He always managed to triumph, but Hera managed to make his life unpleasant until the end.
At that end, however, the gods respected Hercules’ headstrong bravery and suffering so much that they took him up into heaven to dwell with them when he died. There he even made his peace with Hera and married her daughter, Hebe.
And the gods so loved him that they placed upon his chest the Great Globular Cluster, 250,000 suns — a glorious badge of honor.
Tom Burns is the director of Ohio Wesleyan University’s Perkins Observatory, and he would be very happy to answer your questions or sell you a ticket to one of its upcoming Friday-night programs. He can be reached at firstname.lastname@example.org or 740–363‑1257.