The Hercules Constellation: Location, Stars, Deep Sky Objects

Constellations of northern hemisphere spring.
Hercules begins rising in northern hemisphere spring for easy viewing over much of the spring and summer. This chart shows the northern hemisphere spring skies looking north.

Carolyn Collins Petersen 

The Hercules constellation is a lopsided-shaped boxy pattern of stars located in the skies of the northern hemisphere. It's visible in the evening skies from early March to late September each year​ and appears directly overhead at midnight in June. As one of the earliest constellations to be observed, Hercules has a rich history. 

How to Find Hercules

star map to find constellation Hercules
The constellation Hercules is in the evening skies from March through September, visible from nearly everyone on Earth. It is bounded on one side by the small constellation Lyra and the other by the constellation Bo&oumlaut;tes on the other. Its central region is called the "Keystone of Hercules.".  Carolyn Collins Petersen

To find Hercules, look for the center of the constellation, called the Keystone of Hercules. It's the most obvious part of the star pattern. Two running legs appear to be stretched out from the widest part of the Keystone, and two arms are raised high over the narrow end.

Observers in the northern hemisphere should have no problem finding Hercules. For skygazers in the southern hemisphere, it appears much farther north in the sky for individuals as far south as the tip of South America. So, Hercules is visible to most people on the planet except the folks living in Antarctica. It's also hidden in the northern hemisphere regions above the Arctic Circle during the summer months due to the ongoing glare of the Sun, which does not set for several months. 

The Legend of Hercules

ancient hercules
The Roman hero and god Hercules, shown here wrestling the Nemean lion as one of his many labors, was based on the Greek Herakles, also a hero. This is a painting by the artist Pieter Paul Rubens. Image is in public domain, taken by I Sailko, Creative Commons Attribution-Share Alike 3.0. 

The constellation Hercules is based on the legendary exploits of a Greek hero named Heracles, who was based on an even older Babylonian constellation called "Standing Gods." There's some evidence that the star pattern is also somehow associated with the epic of Gilgamesh from Sumerian times. 

Heracles had many adventures and assigned labors by his fellow gods. He also fought many battles. In one battle, he knelt and prayed to his father Zeus for help. The early name of Heracles became "the Kneeler" based on the image of him kneeling in prayer. Eventually, the kneeling hero was connected to Heracles and his many legendary exploits, retold in myths and legends. The Romans then "borrowed" the name for the constellation and renamed it "Hercules."

The Brightest Stars of Hercules

Hercules star chart
A traditional constellation map for Hercules, showing both the IAU boundaries and the bright stars that form the shape of Hercules and his central Keystone. Creative Commons Share-Alike 3.0.

The entire constellation of Hercules includes 22 bright stars that make up the Keystone and his body, plus other stars included in the International Astronomical Union outline of the constellation. These boundaries are set by international agreement and allow astronomers to use common references for stars and other objects in all areas of the sky.

Notice that each star has a Greek letter next to it. The alpha (α) denotes the brightest star, beta (β) the second-brightest star, and so on. The brightest star in Hercules is α Herculis, with the common name of Rasalgethi. It's a double star and its name means "Head of the Kneeler" in Arabic. The star lies about 360 light-years from Earth and is easily visible to the naked eye. Observers who want to see the double need to have a good small telescope. Many stars in the constellation are double stars and some are variable stars (which means they vary in brightness). Here's a list of the best-known:

  • gamma Herculis (double)
  • zeta Herculis (double)
  • kappa Herculis (double)
  • 30 Herculis (variable) 68 Herculis (variable). 

These are all accessible to viewers with good backyard-type telescopes. Beyond the easily found objects, professional astronomers have also found a rich collection of exoplanets and other interesting star types, viewable with professional-grade telescope technology.

Deep Sky Objects in Constellation Hercules

Finder chart for Hercules constellation clusters
Use this chart to spy out the locations of the two globular clusters in Hercules constellation.  Carolyn Collins Petersen

Hercules is best-known for two globular-shaped star clusters that can be observed fairly easily. They're called M13 (M stands for Messier) and M92. These can be spotted with the naked eye under good conditions and look like faint, fuzzy blobs. To get a better view, stargazers should use binoculars or a telescope.​

These two clusters have been studied extensively by astronomers using large observatories as well as the orbiting Hubble Space Telescope. They are interested in learning more about the types of stars in the clusters and counting exactly how many exist in the tight gravitational confines of each cluster.

Visiting M13 in Hercules

M13 globular cluster in the Hercules constellation
M13 is the brightest of the globular clusters in Hercules. This is how it looks through a backyard type telescope. Rawastrodata, via Creative Commons Attribution-Share-Alike 3.0. 

M13 is a fairly bright globular cluster in the constellation Hercules. It's part of a larger population of globulars that orbit the core of our Milky Way Galaxy. This cluster lies about 22,000 light-years away from Earth. Interestingly, scientists once sent a coded data message to this cluster, in the hopes that any civilizations there might receive it. It will arrive in just under 22,000 years.  M92, the other cluster shown on the chart above is about 26,000 light-years away from our planet. 

Stargazers with good telescopes can also seek out these clusters and galaxies in Hercules:

  • NGC 6210 a planetary nebula some 4,000 light-years from Earth
  • NGC 6229: another globular cluster 100,000 light-years from Earth
  • The Hercules Cluster of Galaxies