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Hercules A

Hercules A

Active galaxy in the constellation hercules.Hercules A is super-giant elliptical galaxy.

Hercules constellation is located in the northern sky. It was named after Hercules, the Roman version of the Greek hero Heracles.

Heracles, in turn, was often associated with the Sumerian hero Gilgamesh, and the constellation itself has a long history, dating back to Sumerian times.

Hercules is the fifth largest constellation in the sky, but has no first magnitude stars. In traditional depictions, the star Ras Algethi (Alpha Herculis) represents Hercules’ head and a prominent asterism, the Keystone, marks his torso, as he stands victoriously on Draco’s head.

In mythology, the constellation Hercules is usually associated with the penultimate labour of Heracles, which involved defeating the dragon Ladon, who guarded the garden of the Hesperides. The dragon is represented by the constellation Draco. Hercules constellation was first catalogued by the Greek astronomer Ptolemy in the 2nd century.

Notable deep sky objects in Hercules include the Great Globular Cluster (Messier 13), the globular cluster Messier 92, the planetary nebulae Abell 39 and NGC 6210, the Hercules Cluster of galaxies, and the galaxy cluster Abell 2199.

Facts, location and map

Hercules is the fifth largest constellation. It occupies an area of 1225 square degrees in the sky. The constellation lies in the third quadrant of the northern hemisphere (NQ3) and can be seen at latitudes between +90° and -50°. The neighboring constellations are Aquila, Boötes, Corona Borealis, Draco, Lyra, Ophiuchus, Sagitta, Serpens Caput and Vulpecula.

Hercules belongs to the Hercules family of constellations, along with Aquila, Ara, Centaurus, Corona Australis, Corvus, Crater, Crux, Cygnus, Hydra, Lupus, Lyra, Ophiuchus, Sagitta, Scutum, Sextans, Serpens, Triangulum Australe and Vulpecula.

Hercules contains two Messier objects – Messier 13 (M13, NGC 6205) and Messier 92 (M92, NGC 6341) – and has 12 stars with known planets. The brightest star in the constellation is Kornephoros, Beta Herculis, with an apparent magnitude of 2.81. The Tau Herculids are the only meteor shower associated with the constellation.

The constellation contains 11 formally named stars. The star names approved by the International Astronomical Union (IAU) are Cujam, Franz, Hunor, Irena, Kornephoros, Maasym, Marsic, Ogma, Pipoltr, Rasalgethi, and Sarin.

Hercules constellation map by IAU and Sky&Telescope magazine


Hercules constellation dates back to ancient times. Its origin was unclear even to the Greeks. They knew it as Engonasin, or “the kneeling one.” It was Eratosthenes who identified the kneeler as Heracles, standing over the dragon that guarded the garden of the Hesperides.

Aeschylus associated the constellation with a different tale, describing Heracles as kneeling and exhausted after the battle with the Ligurians.

Heracles was the son of Zeus and Alcmene, a mortal woman. When he was an infant, Zeus laid him at Hera’s breast while she slept. Having suckled her milk, Heracles became immortal. Hera was enraged by this and made Heracles’ life difficult at every turn. She cast a spell that made him lose his mind and turn against his children. Once he regained his senses and realized what he had done, he visited the Oracle at Delphi to see how he could atone for his deed. The Oracle sent him to serve Eurystheus, king of Mycenae, for a period of 12 years. It was then that he got the name Heracles, which means “the glory of Hera.” His given name at birth was Alcides, Alcaeus, or Palaemon according to different sources.

King Eurystheus gave Heracles a series of tasks, known as the Labours of Heracles. The first was to defeated the Nemean lion, a beast with an impenetrable skin. After Heracles had strangled the lion, he used its claws to cut off the skin and later used the pelt as a cloak and the gaping mouth as a helmet, which both protected him and made him look even more frightening. The Nemean lion is represented by the constellation Leo.

The second task was to destroy the Hydra, represented by Hydra constellation, a monster with multiple heads. As he fought with the beast, Hera sent a crab to distract him. Heracles did away with the crab, and Hera placed it in the sky as the constellation Cancer.

Heracles was then sent to catch a deer with golden horns and, after that, a ferocious boar. The fifth task was to clean the stables of King Augeias of Elis. The sixth was to do away with a flock of marauding birds, and the seventh, to catch a bull that breathed fire and was ravaging the land on Crete. The eighth labour was to bring the horses of King Diomedes of Thrace, which ate flesh, to Eurystheus. The ninth was to bring the king the belt of Hippolyte, the queen of the Amazons.

The tenth labour was to steal the cattle of Geryon, a monster that lived on the island of Erytheia. On his way back, he was confronted by local forces that outnumbered and nearly overcame him. He sank to his knees and prayed to Zeus. The god helped him by sending rocks, which Heracles threw at his adversaries. This is the event that, according to Aeschylus, was commemorated by the constellation Engonasin (the kneeler).

Even though Eurystheus and Heracles had originally agreed on ten tasks, when Heracles came back, the king refused to release him from his service and set two additional tasks. The first was to steal the golden apples from Hera’s garden on Mount Atlas. The garden was guarded by the Hesperides, daughters of the titan Atlas, and the Hesperides were guarded by the dragon Ladon, whose task was to make sure that they did not steal any of the apples. The dragon is represented by the constellation Draco. Hera herself placed the dragon in the sky after Heracles had slain it.

The final labour was the most difficult one. Heracles was sent to the gates of the Underworld to fetch Cerberus, the dog that had three heads and was tasked with guarding the entrance and making sure those who had crossed the river Styx did not try to escape. Heracles used his pelt to protect himself and dragged the dog to Eurystheus. The king, who had not expected to see Heracles again, had no choice but to release him.

After completing the twelve labours, Heracles married Deianeira, daughter of King Oeneus. While the two were travelling together, they came to the river Evenus where the centaur Nessus ferried people across. Heracles swam across the river, but Deianeira needed to be carried and Nessus, who offered to do it, fell in lust with her and tried to ravage her. Heracles hit the centaur with an arrow that was tipped in the Hydra’s poison. Before the end, Nessus offered Deianeira some of his blood, saying that it could be used as a love charm. Deianeira kept the blood, poisoned by Heracles’ arrow. Much later, she became worried that Heracles’ attention was wandering to another woman and she gave him a shirt on which she had smeared Nessus’ blood. When Heracles put it on, Hydra’s poison started burning his flesh and, once he realized what was

going on, he built himself a pyre on Mount Oeta and lay on his pelt, ready to meet his end. The fire burned the part of him that was mortal, and the immortal part joined Zeus and the other gods on Mount Olympus. Zeus placed Heracles in the sky as the constellation now known by its Roman name, Hercules.

Hercules stars

ASTERISM: The Keystone

The Keystone asterism is formed by four bright stars in Hercules – Pi, Eta, Zeta, and Epsilon Herculis – and it represents Hercules’ torso.

The Keystone, image: Wikisky

Kornephoros – β Herculis (Beta Herculis)

Beta Herculis, or Kornephoros, is the brightest star in Hercules constellation. Its name comes from Greek and means “the club bearer.” Kornephoros has an apparent magnitude of 2.81 and is approximately 139 light years distant.

Beta Herculis is a suspected variable star, with a visual magnitude that can rise to 2.76. It is not a single but a binary star, one with an orbital period of 410 days.

The primary star in the system is a giant belonging to the spectral class G7 IIIa three times as massive as the Sun and with a radius 17 times solar. The other star in the Beta Herculis system has only 90% of the Sun’s mass.

ζ Herculis (Zeta Herculis)

Zeta Herculis is a multiple star with a combined apparent magnitude of 2.81, only 35 light years distant from Earth. It is the brightest of the four stars that form the Keystone asterism.

The primary component in the system is a subgiant star belonging to the spectral class F9 IV, which is orbited by a smaller companion star at a separation of 1.5 arc seconds, with a period of 34.45 years. The primary star has 2.6 times the Sun’s radius and 1.45 times the solar mass. It is more than six times more luminous than the Sun.

Zeta Herculis was once believed to be a member of the Zeta Herculis moving group, a group of stars that share a common origin and are travelling together in space. The group includes Phi-2 Pavonis in Pavo constellation, Zeta Reticuli in Reticulum, 1 Hydrae in Hydra, Beta Hydri in Hydrus, and Gliese 678 in the constellation Ophiuchus, among other stars.

Sarin – δ Herculis (Delta Herculis)

Delta Herculis is another star system in Hercules, composed of between two and five stars. The primary star is a main sequence subgiant belonging to the spectral class A3 IV, twice the size of the Sun. It has an apparent magnitude of 3.126 and is 75.1 light years distant from the Sun.

π Herculis (Pi Herculis)

Pi Herculis is another star in the Keystone asterism. It is a bright giant star belonging to the spectral class K3 II. It has apparent magnitude of 3.15 and is approximately 377 light years distant from the solar system.

Pi Herculis is 4.5 times more massive than the Sun and has about 60 times the solar radius. It is 1,330 times more luminous than the Sun. The star is classified as a variable and shows variations in luminosity by about 0.0054 magnitudes over every 24 hours. It has an unconfirmed substellar companion.

Rasalgethi – α Herculis (Alpha Herculis)

Alpha Herculis is another multiple star system in Hercules. In a telescope, the system can be resolved into two components. Alpha-1 Herculis has an apparent magnitude of 2.1937 and Alpha-2 Herculis, 5.4. The system is approximately 360 light years distant from Earth. The two components are over 500 astronomical units apart and have an orbital period of roughly 3,600 years.

The primary star in the system is a bright red giant belonging to the spectral class M5IIvar (it is a semi-regular variable), and the secondary component has the stellar classification G5III+F2V. Alpha-2 Herculis is a binary star system composed of a yellow giant and a yellow-white dwarf.

The star’s traditional name, Rasalgethi (or Ras Algethi), comes from the Arabic phrase ra’s al-jaθiyy, which means “the head of the Kneeler.” The “head” association comes from ancient times, when the constellation was depicted upside down on star maps. The star’s Latin name, translated from the Arabic, is Caput Ingeniculi.

Hercules A

Hercules A is an active galaxy in Hercules. It appears to be a regular elliptical galaxy, but when imaged in radio waves, there are plasma jets spanning over a million light years around the galaxy.

The galaxy at the centre, 3C 348, has 1,000 times the mass of the Milky Way Galaxy, and the black hole at its centre is almost 1,000 times more massive than the one at the centre of the Milky Way.

Hercules A is 2,100 million light years distant from Earth.


Further Resources


Biggest Thing in the Universe: The Hercules-Corona Borealis Great Wall (Gamma Ray Burst Wall)


October 15, 2019

NASA - A Multi-Wavelength View of Radio Galaxy Hercules A


Stellar Metamorphosis: A Birthing Galaxy, Hercules A


November 22, 2014

The Hercules Cluster of Galaxies | Science Mission Directorate


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