Hercules (constellation)

Named after the mythological hero, Hercules, it is the fifth largest of the 88 modern constellations. It was also one of Ptolemy's 48 constellations.

Notable features

Constellation of Hercules

Hercules has no first magnitude stars, the brightest being β Herculis (Kornephoros), a yellow giant of spectral type G7IIIa and magnitude 2.78. It has an effective temperature of 4887 K and a radius 17 times larger than that of the Sun. ζ Herculis, the second brightest star in the constellation, is located 35 light years from the solar system and is a binary star made up of a yellow subgiant of type G0IV and a yellow dwarf G7V cooler than the Sun. The orbital period of this system is 34.45 years old. Next in brightness is δ Herculis, called Sarin, a white subgiant of type A1Vn that has a companion that has only been resolved by interferometry. π Herculis is a luminous orange giant—sometimes classified as a supergiant—of spectral type K3II and 4170 K in temperature.

Rasalgethi, despite bearing the Bayer designation Alpha, is only the fifth brightest star in Hercules. It is a complex stellar system whose main component is a cold red luminous giant of type M5II 400 times larger than the Sun. μ Herculis is another stellar system relatively close to Earth, as it is 27.4 light years away. The primary star is a yellow subgiant accompanied by a binary formed by two red dwarfs.

With very different characteristics is φ Herculis, a spectroscopic binary whose main component —a bluish-white star of the main sequence of spectral type B9VspHgMn— is one of the most studied mercury-manganese stars. Its mercury content is about 50,000 times higher than in the Sun. Another chemically peculiar star is ω Herculis, officially called Cujam; of spectral type A2VpCrSr, it has a temperature of 8750 K and a luminosity 55 times that of the Sun.

Among the existing variables in the constellation, g Herculis is a red giant of type M6-III, a semiregular variable of type SRB, wrapped in a layer of circumstellar dust that seems to be composed mainly of iron, magnesium and aluminum oxides, instead of silicates. Helium fusion takes place inside, since it is in the evolutionary stage known as a giant asymptotic branch. X Herculis is another extreme red giant in the final stages of its life, which in the not too distant future will shed its outer layers and become a white dwarf. It is surrounded by a disk-shaped structure detected at radio frequencies. R Herculis and RU Herculis are Mira variables whose respective periods are 240 and 485 days; the second of them is one of the longest periods in this class of variables. Rather, AM Herculis is the prototype of a unique class of cataclysmic variables, called "polars", in which the magnetic field of the primary star—a white dwarf star—completely dominates the accretionary flow of the system.

Hercules has several stars with planetary systems. 14 Herculis is an orange dwarf at 59.2 light-years with two extrasolar planets. Hunor, official name of HD 147506, is an F8V-type star that has a planet detected by astronomical transit whose separation from it is less than 0.07 au. HD 154345 (Gliese 651) is a yellow dwarf with a planet of mass equivalent to 95% of the mass of Jupiter; it moves in an orbit 4.19 AU from the star, its orbital period being approximately 9 years. HD 155358 is a yellow thick disk star of very low metallicity that has two gravitationally interacting planets. Around another yellow dwarf in Hercules, HD 164922, four planets have been detected: one of them is a hot "super-Earth", since the distance that separates it from its star is 10% of that between Earth and the Sun. Likewise, Gliese 649 and Gliese 686 are two red dwarf exoplanets; Gliese 649 b may have a mass similar to Saturn, completing one orbit around the star every 598 days.

This constellation is home to BD+17 3248, one of the oldest known stars with an estimated age of more than 13.4 billion years. It is a highly metal-depleted Population II star in the galactic halo. It belongs to the subclass of stars enriched by neutron capture (r-process).

Another object of interest is GD 362, a white dwarf with a high concentration of heavy metals in its atmosphere that seem to come from a ring of dust that surrounds the star. It has been speculated that the dust disk and heavy elements may have originated from the tidal breakup of an asteroid about 200 km in diameter between 100,000 and a million years ago. Also in Hercules is the ultramassive white dwarf WD 1658+440. With a mass of 1.33 solar masses, it is the most massive white dwarf in the vicinity of the solar system. It has a high temperature of 30,510 K, with an estimated cooling time of 320 million years. It is also an important source of X-rays that appear to come from a homogeneous atmosphere of pure hydrogen.

Image of M92 obtained with the Hubble telescope

Hercules is home to two important globular clusters, M13 and M92. M13 was discovered by Edmond Halley in 1714 and cataloged by Charles Messier in 1764. It consists of 300,000 stars and is 25,100 light-years from Earth. It is thought to originate from the remains of an early galaxy (called Gaia). -Enceladus) that merged with our Milky Way during its early stages of formation. For its part, M92 is 26,700 light years away and is considered one of the oldest clusters. Only sixteen variables have been observed in this cluster, fourteen of which are of RR Lyrae type, while another of which is an eclipsing binary, one of the few present in globular clusters.

Hercules contains two planetary nebulae, NGC 6210 and Abell 39. The first is 5,120 light-years away and its central star has an effective temperature between 50,000 and 69,000 K. The second, very faint, has a spherical shape almost perfect.

In this constellation is found NGC 6207, a spiral galaxy discovered by William Herschel in 1787. NGC 6166 is an elliptical galaxy that is part of the galaxy cluster Abell 2199; 490 million light-years away, it is the main galaxy of the cluster and one of the most luminous galaxies known in terms of X-ray emission. Another galaxy in this constellation, 3C 348, hosts one of the most massive central black holes known, as well as the bright radiosource Hercules A.

On the other hand, the solar apex (point in the sky that indicates the direction in which the Sun moves in its orbit around the center of the galaxy) is located in Hercules, near ξ Herculis.

Main Stars

• α Herculis (Ras Algethi or Rasalgethi), of magnitude 3.31, is a cyntuple star system, whose main star is a variable red giant.
• β Herculis (Kornephoros or Korneforos), the brightest constellation with magnitude 2,78, a giant yellow star.
• γ Herculis, white giant of magnitude 3.74. It is a spectroscopic binary with an orbital period of 11.9 days.
• δ Herculis (Sarin), a white star of magnitude 3,12; it is a binary star whose components have been solved by interferometry.
• ε Herculis, spectroscopic binary of magnitude 3.91.
• ج Herculis (Ruticulus), the second most brilliant constellation with magnitude 2,89, double star formed by two yellow stars of unequal brightness.
• θ Herculis, yellow giant of magnitude 3.49.
• θ Herculis, bright orange giant of magnitude 3,85.
• . Herculis, blue subgiant of magnitude 3,79; three more stars complete this quadruple star system.
• κ Herculis A and κ Herculis B, two giants that form a double optic.
• λ Herculis (Maasym), orange giant of magnitude 4.40.
• μ Herculis, nearby star system that dissociates from the Solar System 27.4 light years. The main star is a yellow sub Giant accompanied by two red dwarfs; a fourth star could complete the system.
• π Herculis, orange giant of magnitude 3,16.

φ Herculis, distant mercury-manganese star 204 light years

• ρ Herculis, a double star whose components, separated 4 seconds of arc, shine with magnitude 4.56 and 5.42.
• σ Herculis, binary whose main component is a white-smoothed star with a dust disk.
• φ Herculis, spectrum binary of magnitude 4,23; its main component is one of the most studied mercury-manganese stars.
• χ Herculis, low metallic yellow dwarf that is 52 light years away.
• ω Herculis (Cujam or Kajam), chemically peculiar star of magnitude 4.57.
• 8 Herculis, white star of magnitude 6,13 that forms a double optic with Kappa Herculis — separation 0.2.o.
• 14 Herculis, orange dwarf at 59.2 light years with a giant planet around. A second partner was discovered in 2006.
• 30 Herculis (g Herculis), red and semi-regular giant whose brightness ranges between magnitude 4.3 and 6.3 in a cycle of 89.2 days.
• 53 Herculis, star of magnitude 5,34 surrounded by a dust disk.
• 50 Herculis, star of magnitude 5.72. It is located at a distance of 283,28 parsec.
• 68 Herculis (u Herculis), an eclipsing binary where there is mass transfer from secondary to primary.
• 72 Herculis (w Herculis), yellow dwarf similar to the Sun 47 light years away.

Image of the system Gliese 623 obtained with the Hubble Space Telescope; Gliese 623 B is on the right of the center.

• 89 Herculis, yellow supergiant in the final stages of his star evolution.
• 95 Herculis, binary star composed of a white giant and a yellow giant separated 6,3 seconds of arc.
• 99 Herculis, low metallic binary whose primary is a yellow dwarf of magnitude 5.20.
• 101 Herculis, a white giant of magnitude 5.11.
• 109 Herculis, orange giant of 3.884 magnitude, the brightest twelfth star of the constellation.
• 110 Herculis, white-yellow star of magnitude 4,20.
• 111 Herculis, a white star of magnitude 4.35.
• X Herculis, a semi-regular pulsating variable whose brightness varies between magnitude 6 and 7 in a period of 95 days.
• SZ Herculis and FN Herculis, ellipsing binaries of magnitude 9,94 and 11,08 respectively.
• UX Herculis, ellipsing binary of magnitude 9,05; during the main eclipse its brightness diminishes 1,16 magnitudes.
• OP Herculis, bright red variable giant between magnitude 5.85 and 6.73.
• HD 147506, yellow subgigante where a massive planet (HAT-P-2b) has been detected in an eccentric orbit near the star.
• HD 149026, yellow dwarf with a planet whose mass is similar to that of Saturn.
• HD 154345, also a yellow dwarf at 58.91 light years with an extrasolar planet.
• HD 155358, low metallic star with two planets that interact gravitationally.
• HD 164922, yellow dwarf with four planets.
• Gliese 623, binary star composed of two red dwarfs.
• Gliese 686 and Gliese 649, red dwarfs at 26.5 and 33.7 light years respectively; in both stars a planet has been detected.
• Gliese 638 and HR 6806, orange dwarfs located respectively 31.9 and 36.2 light years away from Earth.
• GD 362, white dwarf with a ring similar to those of Saturn.

Deep Space Objects

The spectacular globular cluster M13.

Hercules contains two of the most outstanding globular clusters, M13 and M92.

Image of the center of NGC 6210 obtained with the Hubble space telescope.Credits: HST/NASA/ESA.

• M13 (NGC 6205 or Great Hercules Cluster), the brightest globular cluster in the northern hemisphere. Located between γ Herculis and θ Herculis, its joint visual magnitude is 5.80. The variable stars of M13, quite close to Earth at about 25.100 light years, can be observed with amateur telescopes —20 to 30 cm — equipped with CCD cameras.
• M92, also a magnificent globular cluster of magnitude 6,5, is located 6o20' north of π Herculis. It has an extraordinarily low metallicity, approximately 0.5% of the solar; this value indicates an estimated age for this cluster of 14 200 ± 1200, approximately the age of the universe.
• NGC 6166, supermassive elliptical galaxy of CD type, the brightest of the rich cluster of Abell 2199 galaxies.
• NGC 6181, spiral galaxy south of Kornephoros (β Herculis).
• NGC 6207, also spiral galaxy located 30' northeast of M13.
• NGC 6482, elliptical galaxy of magnitude 11,9.
• 3C 348, giant elliptical galaxy with the brilliant Hércules A radius. The central black hole in this galaxy is 1000 times more massive than the Milky Way.
• NGC 6210, planetary nebula located 4th northeast of Kornephoros (β Herculis). Images obtained with the Hubble space telescope allow you to observe hot gas jets that flow through openings in a more ancient and cold gaseous roof.
• Abell 39, planetary nebula with an almost perfect spherical shape. It is 7000 light years away.

Mythology

Image of Hercules or Heracles.

Hercules (in Roman mythology, Heracles in Greek mythology) was a demigod, son of Zeus and Alcmene. He was undoubtedly the greatest hero of the Greeks, known for his superhuman strength. There are many stories about his life, including the account of the twelve labors of Hercules.

This constellation was also known as the kneeling one, and Eratosthenes said that in it Heracles was crushing with one of his knees the serpent that guarded the apples of the Hesperides.

Hyginus mentioned other possibilities of characters with whom the kneeling could be identified: Ceteus, the musician Thamyris blinded by the Muses, Orpheus dying at the hands of Thracian women, Ixion with his arms tied, Prometheus in chains, Hercules fighting with the Ligures or Theseus lifting the stone under which was the sword of his father Aegeus.