Hercules is a large northernconstellation, culminating at midnight in May. It has the fifth largest area of all the constellations. Despite this, it covers a fairly dark area of the sky and has only two stars brighter than third magnitude. It is best known for its deep sky offerings, which include M13, often known as the “Great Globular Cluster of Hercules.” M13 is the brightest globular cluster found at a high declination to the north.
It is also home to another bright globular cluster, M92, as well as the much fainter cluster NGC 6229. The name ‘Hercules’ is the Latin name for the Greek hero Heracles. The constellation is probably much older than any association with Hercules: in the 3rd century BC, Aratus referred to the constellation as representing an unnamed man, but a century later, Eratosthenes identified it as Heracles.
The figure is usually drawn with his foot on the head of the dragon Draco, which is appropriate since one of Hercules’ labors was to kill the dragon that guarded the golden apples that grew in Hera’s garden.
How to find the constellation Hercules
To find Hercules, look for the center of the constellation, called the Keystone of Hercules. It is the most obvious part of the star pattern. The two running legs appear to be stretched out from the widest part of the Keystone, and two arms rise above the narrow end. Observers in the northern hemisphere should have no trouble finding Hercules.
For sky watchers in the southern hemisphere, it appears much further north in the sky for people at the southern tip of South America. Hercules is therefore visible to most people on the planet, except for those living in Antarctica. It is also hidden in regions of the northern hemisphere above the Arctic Circle during the summer months due to the continuous glare of the Sun, which does not set for several months.
Main stars of the Hercules constellation
Zeta
Zeta Herculis is a binary star system about 35 light-years from Earth. The primary star has 50% more mass than the Sun with a radius about 2.5 times greater. Its companion star is a yellow dwarf similar to our Sun.
Sarín
Also known as Delta Herculis, Sarín is a multiple star system located about 75 light-years from Earth. The primary star is a white subgiant with more than twice the radius and mass of our sun.
Kornephoros
Also known as Beta Herculis, Kornephoros is a binary star system about 140 light-years from Earth. The primary star is a yellow giant 17 times larger in diameter than our sun.
Rasalgethi
Also known as Alpha Herculis, Rasalgethi is a multiple star system 360 light-years from Earth. The primary star in the system is a red giant with a radius nearly 400 times that of the sun.
Finding Hercules – Northern Hemisphere
The chart shows the position of Hercules in most of the United States in early summer at 9 pm. This chart can also be applied to other areas of the northern hemisphere such as Canada, the United Kingdom, and Europe.
In April, Hercules will first appear low on the northeastern horizon around 11 p.m. before gradually rising in the sky; by 4 a.m., the constellation will be directly overhead before dipping toward the northwestern horizon.
From May to August, the constellation will be visible from 10 p.m., but it will appear in different parts of the sky depending on the month. In May and June, it will first appear in the northeast or east, and in July and August, it will first appear at the top, before moving toward the northwest horizon as the night progresses.
From September to November, Hercules will first appear in the western night sky between 6 and 9 p.m., depending on the month, before sinking below the northwestern horizon in the following hours.
Finding Hercules – Southern Hemisphere
The table shows the position of Hercules over most of Australia in early winter at 9 p.m. This table can also be applied to other areas of the southern hemisphere such as New Zealand, South Africa, and South America.
In the southern hemisphere, Hercules is visible in the northern night sky.
In June, Hercules becomes visible around 9 p.m. on the northeastern horizon, crossing the night sky toward the northwestern horizon over a period of 6 to 7 hours.
In July and August, it will be visible around 6 and 7 p.m. in the northeastern sky, crossing the night sky before disappearing below the northwestern horizon around midnight.
In September, the constellation will appear in the north around 7 p.m., gradually moving toward the northwestern horizon over the next few hours.
The constellation Hercules is a square pattern of stars located in the skies of the northern hemisphere. It is 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 first constellations observed, Hercules has a rich history.
Mythology of the Hercules constellation
Hercules is a hero in Greek mythology, and his adventures are the basis for several other constellations. Although he is commonly known as Hercules, this is actually the Roman translation of his name from the Greek Heracles.
Hercules was the illegitimate son of Zeus, the King of the Gods. His mother was Alcmene, wife of the Theban general Amphitryon. Zeus disguised himself as Alcmene’s husband to sleep with her, and she later gave birth to twins, one of whom was Hercules, who was fathered by Zeus, the other by her husband. Throughout his life, Hercules was mocked by his stepmother Hera, Zeus’ wife. Her actions eventually drove Hercules mad, leading him to kill his children in a fit of rage.
As a way to atone for his act of madness, Hercules was ordered to carry out twelve labors, which he eventually completed. As a result of the bravery and courage he had shown throughout his life, Hercules became a god after his death.
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The Legend of the Hercules Constellation
The constellation Hercules is based on the legendary exploits of a Greek hero named Heracles, which was based on an even older Babylonian constellation called “Gods Standing.” There is some evidence that the star pattern is also associated in some way with the Epic of Gilgamesh from Sumerian times.
Heracles had many adventures and tasks assigned to him by his fellow gods. He also fought many battles. In one battle, he knelt down and prayed to his father Zeus for help. Heracles’ early name became “the Kneeler” based on the image of him kneeling in prayer. Eventually, the kneeling hero became connected with Heracles and his many legendary exploits, recounted in myths and legends. The Romans later “borrowed” the name of the constellation and renamed it “Hercules.”
The brightest stars in Hercules
The complete constellation of Hercules includes 22 bright stars that make up the Keystone and his body, plus other stars included in the International Astronomical Union’s 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.
Note that each star has a Greek letter next to it. Alpha (α) denotes the brightest star, beta (β) the second brightest star, and so on. The brightest star in Hercules is α Herculis, commonly known as Rasalgethi. It is a double star and its name means “Head of Kneeler” in Arabic.
The star is about 360 light-years from Earth and is easily visible to the naked eye. Observers who want to see the double need a good small telescope. Many stars in the constellation are double stars, and some are variable stars (meaning they vary in brightness). Here is a list of the best known:
- Gamma Herculis (double)
- Zeta Herculis (double)
- Kappa Herculis (double)
All of these are accessible to viewers with good backyard telescopes. Beyond the easy-to-find objects, professional astronomers have also found a rich collection of exoplanets and other types of interesting stars, visible with professional-grade telescope technology.
Deep sky objects in the constellation Hercules
Hercules is best known for two globular star clusters that can be observed quite easily. They are called M13 (M stands for Messier) and M92. These can be seen with the naked eye under good conditions and look like faint, blurry patches. For a better view, astronomers must use binoculars or a telescope.
These two groups have been extensively studied by astronomers using large observatories, as well as the Hubble Space Telescope. They are interested in learning more about the types of stars in the clusters and in counting exactly how many there are within the tight gravitational confines of each cluster.
Visiting M13 in Hercules
M13 is a fairly bright globular cluster in the constellation Hercules. It is part of a larger population of globular clusters orbiting the core of our Milky Way. This group is located about 22,000 light-years from Earth. Interestingly, scientists once sent a message of encoded data to this group, hoping that civilizations there might receive it. It will arrive in just under 22,000 years. M92, the other group shown in the table above, is about 26,000 light-years from our planet.
Astronomers with good telescopes can also look for these clusters and galaxies in Hercules:
- NGC 6210, a planetary nebula about 4,000 light-years from Earth
- NGC 6229: another globular cluster 100,000 light-years from Earth
- The Hercules group of galaxies
