Hercules
What is Hercules?
Constellations· Summer evenings (N) · the Keystone between Vega and Arcturus. The kneeling hero Heracles: the fifth-largest constellation, but with no bright stars, so it is found by the four-star trapezoid of his body, the Keystone. On one side of the Keystone sits the globular cluster M13, visible as a faint haze in binoculars.
📍 Visible from where you are right now — computed in your browser
Stars of the figure
| Star | Magnitude |
|---|---|
| Rasalgethi | 3.1 |
The 1 brightest of the 18 stars used in the figure (19 lines). Lower magnitude means brighter.
Deep-sky objects near this constellation
Constellation basics
| Season | summer evenings, June–August |
|---|---|
| Brightest star | Kornephoros (2.8) |
| How to find | the four-star trapezoid, the Keystone, midway between Vega and Arcturus |
| Area rank | 5th of 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Where the solar system is heading — the solar apex in Hercules
The Sun is not standing still. The whole solar system moves at about 20 km per second relative to the neighbouring stars, and the direction is Hercules. This point, not far from Vega, is called the solar apex. William Herschel first worked it out in 1783 by comparing how many stars move across the sky.
His method is like walking down an avenue of trees. The trees ahead seem to spread apart to either side, while those behind seem to close together. Herschel found the stars doing the same: drawing apart in one direction and crowding together in the opposite one. The side where they spread apart is where we are heading.
Twenty kilometres a second is about 600 million kilometres a year, roughly four times the distance from Earth to the Sun. While Earth circles the Sun, it is also carried forward that far every year. So Earth's real path through space is not a closed circle but a stretched-out spiral, like a pulled spring. This motion is separate from the much faster rotation of the whole galaxy, about 220 km per second.
The constellation in depth
Hercules shows the hero of the twelve labours down on one knee. The ancient Greeks first knew the figure only as ‘the Kneeler’, without a name. Later they saw him as Heracles standing on the dragon Ladon, and his foot does rest right beside the head of Draco. Seen from the northern hemisphere he is upside down, with his head to the south and his feet toward the pole.
On the western side of the Keystone lies M13, a globular cluster: a ball of hundreds of thousands of stars packed tightly together. It is 25,000 light-years away, so the light we see tonight left it 25,000 years ago. In 1974 the Arecibo radio telescope in Puerto Rico beamed a message for other civilisations toward this cluster. It will take just as long to arrive.
On summer evenings, look halfway between Vega overhead and Arcturus in the west for four stars in a trapezoid. This is the Keystone, and the hero's arms and legs spread out from it. About a third of the way along its western side, binoculars show M13 as a small ball of cotton. Set the Sky view to a July night with deep-sky objects on, and the cluster is marked.
Frequently asked
- When can I see Hercules?
- Hercules is best seen in summer evenings, June–August.
- How do I find Hercules?
- To find Hercules, look for the four-star trapezoid, the Keystone, midway between Vega and Arcturus.
- What is the brightest star in Hercules?
- The brightest star in Hercules is Rasalgethi, at magnitude 3.1.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.