The Hercules constellation is one of the night sky’s largest figures, representing the mythological hero of immense strength. It is one of the 88 modern constellations and a popular target for stargazers, especially in the Northern Hemisphere. Finding Hercules requires looking for a recognizable pattern of stars due to its distinctive shape and the stunning deep-sky objects it contains.
Defining the Hercules Constellation
Hercules is formally recognized by the International Astronomical Union (IAU) with the official abbreviation “Her.” Ranking as the fifth largest of all 88 constellations, it spans 1,225 square degrees of the night sky. Hercules is best viewed during the summer months from mid-northern latitudes, culminating highest in the sky around July.
The constellation’s location near the celestial equator allows it to be visible from latitudes between +90° and −39°. Despite its size, Hercules is known for its relatively dim stars, containing none of the first or second magnitude. Its brightest star is Beta Herculis (Kornephoros), a yellow giant with an apparent magnitude of 2.81. Alpha Herculis (Rasalgethi), a variable red giant, is also notable, and its name translates to “the kneeler’s head.”
Identifying the Keystone Asterism
To visually locate Hercules, observers look for its most prominent feature, the “Keystone.” This recognizable pattern of stars forms the hero’s torso as a distinct, lopsided quadrilateral shape. The Keystone is composed of four stars: Pi Herculis, Eta Herculis, Zeta Herculis, and Epsilon Herculis.
The best way to find this pattern is to look between the two bright summer stars, Vega (in Lyra) and Arcturus (in Boötes). The Keystone appears about one-third of the way from Vega to Arcturus and is most easily observed when the constellation is high in the sky during summer evenings.
Alpha Herculis (Rasalgethi) is positioned outside the Keystone, marking the hero’s head. The Keystone is essential because the constellation’s other stars can be challenging to see, especially in light-polluted areas. Once this trapezoid is identified, the rest of the figure, often depicted as the kneeling hero, can be mentally traced.
Notable Deep-Sky Features
The Hercules constellation is home to two primary deep-sky targets: the globular clusters Messier 13 (M13) and Messier 92 (M92). M13, often called the Great Globular Cluster in Hercules, is the most well-known. It is a dense, spherical collection of several hundred thousand stars orbiting the center of the Milky Way galaxy.
M13 is located within the Keystone asterism, found between the stars Eta and Zeta Herculis. With an apparent magnitude of 5.8, it is faintly visible to the naked eye under dark conditions. Through binoculars or a small telescope, M13 appears as a bright, fuzzy patch that resolves into countless pinpoints of light at higher magnification.
M92 is the second significant deep-sky object, slightly smaller and dimmer than M13, with an apparent magnitude of 6.4. Both M13 and M92 are massive, ancient stellar cities that contrast sharply with the relatively dim stars forming the constellation’s outline.
The Mythological Origin
The figure of Hercules originates from Greek mythology, where the hero Heracles was the son of Zeus and the mortal Alcmene. Ancient observers originally knew the constellation as Engonasin, meaning “the Kneeler,” before the Roman adaptation of the name Hercules. The mythological depiction shows the hero in a kneeling posture, sometimes struggling with the dragon Draco.
One traditional story suggests the constellation represents Heracles praying to Zeus during a battle, giving rise to the “Kneeler” name. Another visualization shows him wearing the skin of the Nemean Lion and holding his club. The constellation immortalizes the hero, famous for completing his twelve arduous labors.