Hercules (constellation)

Hercules is a constellation named after Hercules, the Roman mythological hero adapted from the Greek hero Heracles. Hercules was one of the 48 constellations listed by the second-century astronomer Ptolemy, and it remains one of the 88 modern constellations today. It is the fifth-largest of the modern constellations and is the largest of the 50 which have no stars brighter than apparent magnitude +2.5.

Characteristics

Hercules is bordered by Draco to the north; Boötes, Corona Borealis, and Serpens Caput to the east; Ophiuchus to the south; Aquila to the southwest; and Sagitta, Vulpecula, and Lyra to the west. Covering 1225.1 square degrees and 2.970% of the night sky, it ranks fifth among the 88 constellations in size.^[2] The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is 'Her'.^[3] The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of 32 segments (illustrated in infobox). In the equatorial coordinate system, epoch 2000, the right ascension coordinates of these borders lie between 16^h 00^m 26.64^s and 18^h 57^m 49.50^s, while the declination coordinates are between +3.67° and +51.32°.^[4] In mid-northern latitudes, Hercules is best observed from mid-spring until early autumn, culminating at midnight on June 13.^[1]

The

Hercules has no

Mu Herculis is 27.4 light-years from Earth. The solar apex, i.e., the point on the sky which marks the direction that the Sun is moving in its orbit around the center of the Milky Way, narrowly figures in Hercules,^[11] between his more outstretched foot (Omicron Herculis) and Vega (in neighboring Lyra).

Planetary systems

Fifteen stars in Hercules are known to be orbited by

• 14 Herculis has two planets. The planet 14 Herculis b had the longest period (4.9 years)^[12] and widest orbit (2.8 AU) at the time of discovery. The planet 14 Herculis c orbits much further out with very low eccentricity. It was discovered in 2005 but was only confirmed in 2021.^[13][14]
• transiting hot Jupiter planet.^[15]
• HD 154345 has the planet HD 154345 b, a long period (9.095 years) and wide orbit (4.18 AU).
• semimajor axis of 2.11 AU.^[16] More planets have been discovered since.^[17][14]
• HD 147506 has the most massive transiting planet HAT-P-2b at the time of discovery.^[18] The mass is 8.65 M_J.
• HD 155358 has two planets around the lowest metallicity planet-harboring star (21% Sun). Both planets orbit in mild eccentricities.^[19]
• GSC 03089-00929 has a short transiting planet TrES-3b. The period was 31 hours.
• Gliese 649 has a saturnian planet around the red dwarf star.^[20]
• HD 156668 has an Earth mass planet with a minimum mass of four Earth masses.^[21]
• HD 164595 is a G-type star with one known planet, HD 164595 b.^[22][23]
• TOI-561 has four, or possibly five planets. The innermost of which, TOI-561 b, is notable because it is an ultra-short period planet.

Deep-sky objects

Hercules contains two bright

M13, visible to both the naked eye and binoculars, is a globular cluster of the 6th magnitude that contains more than 300,000 stars and is 25,200 light-years from Earth. It is also very large, with an apparent diameter of over 0.25 degrees, half the size of the full moon; its physical diameter is more than 100 light-years. Individual stars in M13 are resolvable in a small amateur telescope.^[10]

M92 is a globular cluster of magnitude 6.4, 26,000 light-years from earth. It is a Shapley class IV cluster, indicating that it is quite concentrated at the center; it has a very clear nucleus.^[24] M92 is visible as a fuzzy star in binoculars, like M13; it is denser and smaller than the more celebrated cluster. The oldest globular cluster known at 14 billion years, its stars are resolvable in a medium-aperture amateur telescope.^[10]

NGC 6229 is a dimmer globular cluster, with a magnitude of 9.4, it is the third-brightest globular in the constellation. 100,000 light-years from Earth, it is a Shapley class IV cluster, meaning that it is fairly rich in the center and quite concentrated at the nucleus.^[25]

NGC 6210 is a planetary nebula of the 9th magnitude, 4000 light-years from Earth visible as a blue-green elliptical disk in amateur telescopes larger than 75 mm in aperture.^[10]

The Hercules Cluster (Abell 2151) is a cluster of galaxies in Hercules.

The brightest radio source in the constellation is Hercules A, an elliptical galaxy located 2.1 billion light years away with a supermassive black hole with a mass of 2.5-billion-solar-mass that has radio jets that extend for one-and-a-half million light-years.^[31] Another bright radio source in Hercules is the quasar 3C 345 which has a jet that appears to move faster than the speed of light.^[32]

The Hercules–Corona Borealis Great Wall, the largest structure in the universe, is in Hercules.

Visualizations

Traditional

The traditional visualization imagines

A common form found in modern star charts uses the quadrangle formed by π Her, η Her, ζ Her and ε Her (known as the "Keystone" asterism) as Hercules's torso.

H.A. Rey

H. A. Rey has suggested an alternative visualization in which the "Keystone" becomes Hercules's head. This quadrangle lies between two very bright stars: Vega in the constellation Lyra and α CrB (Alphecca) in the constellation Corona Borealis. The hero's right leg contains two bright stars of the third magnitude: α Her (Rasalgethi) and δ Her (Sarin). The latter is the right knee. The hero's left leg contains dimmer stars of the fourth magnitude which do not have Bayer designations but which do have Flamsteed numbers. The star β Her belongs to the hero's outstretched right hand, and is also called Kornephoros.

History

According to Gavin White, the Greek constellation of Hercules is a distorted version of the Babylonian constellation known as the "Standing Gods" (MUL.DINGIR.GUB.BA.MESH). White argues that this figure was, like the similarly named "Sitting Gods", depicted as a man with a serpent's body instead of legs (the serpent element now being represented on the Greek star map by the figure of Draco that Hercules crushes beneath his feet). He further argues that the original name of Hercules – the 'Kneeler' (see below) – is a conflation of the two Babylonian constellations of the Sitting and Standing Gods.^[34]

The earliest Greek references to the constellation do not refer to it as Hercules. Aratus describes it as follows:

Right there in its [Draco's] orbit wheels a Phantom form, like to a man that strives at a task. That sign no man knows how to read clearly, nor what task he is bent, but men simply call him On His Knees. [Ἐγγόνασιν "the Kneeler"].^[35]

Now that Phantom, that toils on his knees, seems to sit on bended knee, and from both his shoulders his hands are upraised and stretch, one this way, one that, a fathom's length. Over the middle of the head of the crooked Dragon, he has the tip of his right foot. Here too that Crown [Corona], which glorious Dionysus set to be memorial of the dead Ariadne, wheels beneath the back of the toil-spent Phantom. To the Phantom’s back the Crown is near, but by his head mark near at hand the head of Ophiuchus [...] Yonder, too, is the tiny Tortoise, which, while still beside his cradle, Hermes pierced for strings and bade it be called the Lyre [Lyra]: and he brought it into heaven and set it in front of the unknown Phantom. That Croucher on his Knees comes near the Lyre with his left knee, but the top of the Bird’s head wheels on the other side, and between the Bird’s head and the Phantom’s knee is enstarred the Lyre.^[36]

The story connecting Hercules with the constellation is recounted by Dionysius of Halicarnassus:

On his way back to

Hyginus^[38]

Hercules is also sometimes associated with Gilgamesh, a Sumerian mythological hero.^[10]

Equivalents

In

Arab translators of Ptolemy named it in Arabic: الرقيس, romanized: al-raqis, lit. 'the player'^[citation needed] (not to be confused with Arabic: الراقص, romanized: al-rāqiṣ, lit. 'the trotting (camel), the dancing one'), the name for the star Mu Draconis.^[39][40] Hence its Swahili name Rakisi.^{[citation needed]}

See also

• Hercules (Chinese astronomy)

References

Further reading

• ISBN 0-395-24830-2
  .
• Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London.
  ISBN 978-0-691-13556-4
  .

External links

Wikimedia Commons has media related to:
Hercules (constellation) (category)

• The Deep Photographic Guide to the Constellations: Hercules
• The clickable Hercules
• Star Tales – Hercules
• Warburg Institute Iconographic Database (ca 160 medieval and early modern images of Hercules)