Hercules
Hercules, the fifth-largest constellation in the sky. This greatest of heroes holds the trapezoidal "Keystone" and the beautiful globular cluster M13.
Science
The scienceHercules is the fifth-largest constellation in the sky, but with few bright stars, the trick is to first find the trapezoidal "Keystone" at its center. Along one side of this Keystone lies "M13," counted as the finest globular cluster of the northern hemisphere, a body of about 300,000 stars packed together like a ball, visible even to the naked eye as a faint glow. In 1974 the Arecibo radio telescope aimed at this very M13 to beam out the "Arecibo message," the first interstellar message sent to any alien civilization.
Mythology
How it became a constellationHercules, born the son of Zeus, was the greatest hero of Greece. To atone for the crimes he committed in a madness inflicted by the goddess Hera's curse, he completed twelve labors, facing the Nemean Lion, the water serpent Hydra, and the dragon that guarded the golden apples, among others. In the sky he is drawn kneeling on one knee, his foot pressing down on the head of Draco, which for a long time earned him only the name "the Kneeler."
Observing Guide
how to observe🔭 How to find it
On a summer night, look about midway between Arcturus (the bright star of Boötes) and Vega (in Lyra), and you'll spot a trapezoid of four stars known as the "Keystone." This Keystone sits at the very center of Hercules's body; since the constellation has few bright stars and its outline is faint, finding this trapezoid first is the key. From the Keystone, the stars of the arms and legs stretch out in all directions.
✨ What to look for
Hercules's pride is M13 (the Great Hercules Cluster), considered the finest globular cluster in the Northern Hemisphere. It sits on the western side of the Keystone, making it easy to locate; some 300,000 stars are bunched into a ball, visible even to the naked eye as a faint smudge under a dark sky, and a telescope resolves it star by star right to the edges. A little way off lies another superb globular, M92, so you can compare the two in a single night.
📍 Where to see it (US · Canada · UK · Australia)
Ranging from about +14° to +39° in declination, Hercules is a summer constellation that climbs high toward the zenith from the US, Canada, and the UK on nights from May through September, giving superb, steady views of the globular cluster M13. From Australia it sits low in the northern sky during the southern winter, with the Keystone barely clearing the horizon, so northern observers have by far the better view.