Hercules: The Kneeling Giant in the Sky

Hercules is one of the oldest constellations recognized in the night sky, yet it often goes overlooked by casual observers. Unlike its flashier neighbors, Hercules lacks any first-magnitude stars to immediately draw the eye. What it does offer is a fascinating collection of deep sky objects, a rich mythological heritage, and a distinctive asterism called the Keystone that serves as a gateway to some of the finest globular clusters visible from the Northern Hemisphere. You can locate Hercules at any time by opening StarGlobe and pointing your device toward the sky.

Finding Hercules in the Night Sky

The easiest way to locate Hercules is to find the bright star Vega in Lyra and the equally brilliant Arcturus in Bootes. Hercules sits roughly between these two beacons. The constellation occupies a large area of sky, ranking as the fifth-largest of the 88 modern constellations at 1,225 square degrees, but its stars are relatively faint, with the brightest being Kornephoros (Beta Herculis) at magnitude 2.8.

The key to recognizing Hercules is the Keystone, a slightly lopsided quadrilateral of four stars that forms the hero's torso. Once you identify this trapezoidal shape, the rest of the constellation falls into place. Two lines of stars extend from the Keystone to represent the arms and legs of the kneeling figure. From mid-northern latitudes, Hercules is best placed for evening observation during June, July, and August, when it passes nearly overhead. Check our summer sky guide for more about what to observe during warm months.

The Keystone Asterism

The Keystone is formed by four stars: Eta Herculis, Pi Herculis, Epsilon Herculis, and Zeta Herculis. While none of these is particularly bright, the pattern is distinctive enough to pick out once you know where to look. The Keystone is important not just for identifying the constellation but also because it points toward two remarkable globular clusters that make Hercules a favorite target for telescope users.

To find the clusters, look along the western edge of the Keystone, between Eta and Zeta Herculis. Approximately one-third of the way from Eta to Zeta lies M13, the Great Globular Cluster. On the opposite side of the Keystone, between Pi and Eta, sits the slightly fainter M92.

The Great Globular Cluster M13

M13 is one of the finest globular clusters in the northern sky and a showpiece object for amateur astronomers. Located about 25,000 light-years from Earth, this dense ball of roughly 300,000 stars spans about 145 light-years in diameter. On a clear, dark night, M13 is visible to the naked eye as a faint fuzzy spot. Through binoculars it becomes an obvious smudge, and a moderate telescope begins to resolve individual stars around the cluster's edges, creating a breathtaking view.

M13 gained additional fame in 1974 when the Arecibo radio telescope transmitted a coded message toward the cluster as part of a demonstration of human technological achievement. The message contained basic information about humanity, our solar system, and DNA. Given the cluster's distance, any reply would take at least 50,000 years for a round trip. If you enjoy hunting deep sky objects, our guide to Messier objects for beginners provides a broader introduction.

M92 and Other Deep Sky Objects

M92 is often overshadowed by its more famous neighbor, but it is an exceptional globular cluster in its own right. At magnitude 6.3, it is only slightly fainter than M13 and would be the highlight of any other constellation. M92 lies about 27,000 light-years away and is one of the oldest known globular clusters, with an estimated age of around 14 billion years, making it nearly as old as the universe itself.

Hercules also contains Abell 2151, known as the Hercules Galaxy Cluster, a collection of roughly 200 galaxies located about 500 million light-years away. This is a challenging target requiring large amateur telescopes and dark skies, but it rewards patient observers with a field full of faint galactic smudges.

Notable Stars in Hercules

Kornephoros (Beta Herculis) is the constellation's brightest star at magnitude 2.8. The name comes from a Greek word meaning "club-bearer." It is a yellow giant star about 139 light-years from Earth. Rasalgethi (Alpha Herculis) is actually slightly fainter than Beta despite carrying the alpha designation. Rasalgethi is a striking double star, with a red supergiant primary and a blue-green secondary that create a beautiful color contrast in a telescope.

Zeta Herculis is another fine double star, with components separated by just 1.5 arcseconds. It requires steady seeing and moderate magnification to split, making it a satisfying challenge for observers. If double stars interest you, Hercules offers several rewarding pairs to explore.

Mythology and History

The constellation is named after the Roman hero Hercules, known to the Greeks as Heracles. He was the son of Zeus and the mortal woman Alcmene, and he was renowned for his extraordinary strength. The most famous stories involve his Twelve Labors, a series of seemingly impossible tasks he performed as penance. These included slaying the Nemean Lion (represented by the constellation Leo), killing the multi-headed Hydra (the constellation Hydra), and capturing various mythical beasts.

The constellation's depiction as a kneeling figure predates its association with Hercules. The ancient Greeks originally called it "the Kneeler" without attaching a specific identity. Over time, the figure became associated with Heracles, particularly showing him in combat with the Lernaean Hydra or resting after his labors. On old star maps, he is typically shown upside down, with his feet near the celestial north pole and his head pointing southward.

The Solar Apex

Hercules holds a special significance in modern astronomy because the solar apex, the point in the sky toward which our Sun and solar system are moving, lies within its boundaries. The Sun is traveling toward a point near the star Vega at roughly 20 kilometers per second relative to nearby stars, and this direction falls in the western portion of Hercules. So when you gaze at this constellation, you are looking in the direction of our cosmic journey.

Observing Tips

Because Hercules lacks very bright stars, it is best observed from locations with reasonably dark skies. Start by identifying Vega and Arcturus, then look for the Keystone in the space between them. Binoculars are helpful for confirming the Keystone shape and for locating M13. Even from suburban skies, M13 is rewarding through a small telescope. For those interested in learning how to start stargazing, Hercules is an excellent constellation to practice star-hopping techniques.

The constellation is circumpolar from latitudes above about 60 degrees north, meaning it never sets. For most mid-latitude observers, Hercules is above the horizon for the majority of the night during summer. Use StarGlobe to track the Keystone and its treasures throughout the evening, and discover why this ancient kneeling figure remains a highlight of the summer sky.