The constellation Hercules as it may appear to thenaked eye.
Hercules is bordered byDraco to the north;Boötes,Corona Borealis, andSerpens Caput to the west;Ophiuchus to the south;Aquila to the southwest; andSagitta,Vulpecula, andLyra to the east. 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 theInternational Astronomical Union in 1922, is 'Her'.[3] The official constellation boundaries, as set byEugène Delporte in 1930, are defined by a polygon of 32 segments (illustrated in infobox). In theequatorial coordinate system, epoch 2000, theright ascension coordinates of these borders lie between16h 00m 26.64s and18h 57m 49.50s, while thedeclination 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]
Thesolar apex is the direction of the open motion with respect to theLocal Standard of Rest. This is located within the constellation of Hercules, around coordinates right ascension18h 00m and declination 30° 00′.[5] The north pole of thesupergalactic coordinate system is located within this constellation at right ascension18h 55m 01s and declination +15° 42′ 32″.[6]
Hercules has nofirst or second magnitude stars. However, it does have several stars above magnitude 4.Alpha Herculis, traditionally called Rasalgethi, is atriple star system, partly resolvable in small amateur telescopes, 359 light-years from Earth. Its common name means "the kneeler's head".[7] The primary is an irregularvariable star; it is abright giant with a minimum magnitude of 4 and a maximum magnitude of 3. It has a diameter of roughly 400solar diameters.[8] The secondary, aspectroscopic binary that orbits the primary every 3600 years, is a blue-green hued star of magnitude 5.6.Beta Herculis, also called Kornephoros, is the brightest star in Hercules. It is ayellow giant of magnitude 2.8, 148 light-years from Earth; kornephoros means club-bearer.[9]Delta Herculis A is a double star divisible in small amateur telescopes. The primary is a blue-white star of magnitude 3.1, and is 78 light-years from Earth. The optical companion is of magnitude 8.2.Gamma Herculis is also a double star divisible in small amateur telescopes. The primary is awhite giant of magnitude 3.8, 195 light-years from Earth. The optical companion, widely separated, is 10th magnitude.Zeta Herculis is a binary star that is becoming divisible in medium-aperture amateur telescopes, as the components widen to their peak in 2025. The system, 35 light-years from Earth, has a period of 34.5 years. The primary is a yellow-tinged star of magnitude 2.9 and the secondary is an orange star of magnitude 5.7.[10]
Hercules hosts further quite bright double stars and binary stars.Kappa Herculis is a double star divisible in small amateur telescopes. The primary is a yellow giant of magnitude 5.0, 388 light-years from Earth; the secondary is anorange giant of magnitude 6.3, 470 light-years from Earth.Rho Herculis is a binary star 402 light-years from Earth, divisible in small amateur telescopes. Both components are blue-green giant stars; the primary is magnitude 4.5 and the secondary is magnitude 5.5.95 Herculis is a binary star divisible in small telescopes, 470 light-years from Earth. The primary is a silvery giant of magnitude 4.9, and the secondary is an old, reddish giant star of magnitude 5.2. The star HD164669 near the primary may be an optical double.100 Herculis is a double star easily divisible in small amateur telescopes. Both components are magnitude 5.8 blue-white stars; they are 165 and 230 light-years from Earth.[10]
There are several dimmervariable stars in Hercules.30 Herculis, also called g Herculis, is asemiregularred giant with a period of 3 months. 361 light-years from Earth, it has a minimum magnitude of 6.3 and a maximum magnitude of 4.3.68 Herculis, also called u Herculis, is aBeta Lyrae-typeeclipsing binary star. 865 light-years from Earth, it has a period of 2 days; its minimum magnitude is 5.4 and its maximum magnitude is 4.7.[10]
Mu Herculis is 27.4light-years from Earth. Thesolar apex, i.e., the point on the sky which marks the direction that the Sun is moving in its orbit around the center of theMilky Way, narrowly figures in Hercules,[11] between Hercules' left elbow (nearOmicron Herculis) andVega (in neighboringLyra).
14 Herculis has two planets. The planet14 Herculis b had the longest period (4.9 years)[12] and widest orbit (2.8AU) at the time of discovery. The planet14 Herculis c orbits much further out with very low eccentricity. It was discovered in 2005 but was only confirmed in 2021.[13][14]
Hercules contains two brightglobular clusters:M13, the brightest globular cluster in the northern hemisphere[dubious –discuss], andM92. It also contains the nearly sphericalplanetary nebulaAbell 39. M13 lies between the starsη Her andζ Her; it is dim, but may be detected by the unaided eye on a very clear night.
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 thefull 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 aplanetary 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]
AT2018cow, a large astronomical explosion detected on 16 June 2018.[26][27] As of 22 June 2018, thisastronomical event has generated a very large amount of interest among astronomers throughout the world[28] and may be, as of 22 June 2018, considered a supernova tentatively namedSupernova 2018cow.[29][30]
TheHercules Cluster (Abell 2151) is a cluster of galaxies in Hercules.
The traditional visualization imaginesα Herculis as Hercules's head; its name,Rasalgethi, literally means "head of the kneeling one". Hercules's left hand then points toward Lyra from his shoulder (δ Herculis), andβ Herculis, or Kornephoros ("club-bearer") forms his other shoulder. His narrow waist is formed byε Herculis andζ Herculis. His right leg is kneeling. Finally, his left leg (withθ Herculis as the knee andι Herculis the foot) is stepping on Draco's head, the dragon/snake whom Hercules has vanquished and perpetually gloats over for eternities.[33]
An alternative way to connect the stars of the constellation Hercules, suggested byH.A. Rey. Here, Hercules is shown with his head at the top.Hercules as depicted inUrania's Mirror, a set of constellation cards published in London c.1825. The figure appears upside down in the sky relative to neighbouring constellations. Theformer constellation ofCerberus is held by Hercules before its stars were part of the constellation.
A common form found in modern star charts uses the quadrangle formed byπ Her,η Her,ζ Her andε Her (known as the "Keystone"asterism) as the lower half (abdomen) of Hercules's torso.
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 andα CrB (Alphecca) in the constellationCorona Borealis. The hero's right leg contains two bright stars of the third magnitude:α Her (Rasalgethi) andδ Her (Sarin). The latter is the right knee. The hero's left leg contains dimmer stars of the fourth magnitude which do not haveBayer designations but which do haveFlamsteed numbers. The starβ Her belongs to the hero's outstretched right hand, and is also called Kornephoros.
According to Gavin White, the Greek constellation of Hercules may be 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 ofDraco 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] Alternatively, it is possible that a large part of Hercules comprised another Babylonian constellation, the Sitting Dog (MUL.UR.GI).[35]
The constellation is also sometimes associated withGilgamesh, aSumerian mythological hero.[10]Phoenician tradition is said to have associated this constellation with their sun god, who slew a dragon (Draco).[36]
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"].[37]
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.[38]
The constellation is connected with Hercules inDe astronomia (probably 1st century BCE/CE, and attributed toHyginus), which describes several different myths about the constellation:
Eratosthenes (3rd century BCE) is said to have described it as Hercules, placed above Draco (representing the dragon of theHesperides) and preparing to fight it, holding his lion's skin in his left hand, and a club in his right (this can be found in theEpitome Catasterismorum[39]).
Panyassis'Heracleia (5th century BCE) reportedly saidJupiter was impressed by this fight, and made it a constellation, with Hercules kneeling on his right knee, and trying to crush Draco's head with his left foot, while striking with his right hand and holding the lion skin in his left.
Araethus (3rd/4th century BCE) is said to have described the constellation as depictingCeteus son ofLycaon, imploring the gods to restore his daughterMegisto who had been transformed into a bear.
Hegesianax (2nd/3rd century BCE), who it says describes it asTheseus lifting the stone atTroezen.
Anacreon of Alexandria, who it claims also supports the idea that it depicts Theseus, saying that the constellationLyra (said to be Theseus' lyre in other sources) is near Theseus.
Thamyris blinded by theMuses, kneeling in supplication.
Aeschylus' lost playPrometheus Unbound (5th century BCE), which recounted that when Hercules drives the cattle ofGeryon throughLiguria (northernItaly), the Ligurians will join forces and attack him, attempting to steal the cattle. Hercules fights until his weapons break, before falling to his knees, wounded. Jupiter, taking pity on his son, provides many stones on the ground, which Hercules uses to fight off the Ligurians. In commemoration of this, Jupiter makes a constellation depicting Hercules in his fighting form. (A quote from this section of the play is preserved inDionysius of Halicarnassus'Roman Antiquities: "And thou shalt come to Liguria's dauntless host, Where no fault shalt thou find, bold though thou art, With the fray: 'tis fated thy missiles all shall fail."[40])
Ixion with his arms bound for trying to attackJuno.
TheScholia to Aratus mention three more mythical figures in connection with this constellation:Sisyphus orTantalus, who suffered inTartarus for having offended the gods, orSalmoneus, who was struck down byZeus for his hubris.[39] Another classical author associated the constellation withAtlas.[36]
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 starMu Draconis.[42][43]Hence its Swahili nameRakisi.[citation needed]
^Kaler, Jim (4 May 2007)."Rasalgethi".STARS, University of Illinois. Retrieved6 July 2019.
^Moravveji, Ehsan; Guinan, Edward F.; Khosroshahi, Habib; Wasatonic, Rick (December 2013), "The Age and Mass of the α Herculis Triple-star System from a MESA Grid of Rotating Stars with 1.3 <= M/M ⊙ <= 8.0",The Astronomical Journal,146 (6): 13,arXiv:1308.1632,Bibcode:2013AJ....146..148M,doi:10.1088/0004-6256/146/6/148,S2CID117872505, 148.
^Kaler, Jim."Kornephoros".STARS, University of Illinois. Retrieved6 July 2019.
^abRosenthal, Lee J.; Fulton, Benjamin J.; Hirsch, Lea A.; Isaacson, Howard T.; Howard, Andrew W.; Dedrick, Cayla M.; Sherstyuk, Ilya A.; Blunt, Sarah C.; Petigura, Erik A.; Knutson, Heather A.; Behmard, Aida; Chontos, Ashley; Crepp, Justin R.; Crossfield, Ian J. M.; Dalba, Paul A.; Fischer, Debra A.; Henry, Gregory W.; Kane, Stephen R.; Kosiarek, Molly; Marcy, Geoffrey W.; Rubenzahl, Ryan A.; Weiss, Lauren M.; Wright, Jason T. (2021), "The California Legacy Survey. I. A Catalog of 178 Planets from Precision Radial Velocity Monitoring of 719 Nearby Stars over Three Decades",The Astrophysical Journal Supplement Series,255 (1): 8,arXiv:2105.11583,Bibcode:2021ApJS..255....8R,doi:10.3847/1538-4365/abe23c,S2CID235186973
^ab"Hercules".Star Myths of the Greeks and Romans: A Sourcebook. Translated by Condos, Theony. Grand Rapids: Phanes Press. 1997. p. 117.ISBN9781890482930.
^"Ἐγγόνασιν (ἐν γόνασιν), Arat. 66, 669, Gal. 9. 936, etc."[1] Henry George Liddell and Robert Scott.A Greek-English Lexicon. Oxford. Clarendon Press, 1940.
^AratusPhaenomena, trans. Mair, A. W. & G. R. Loeb Classical Library Volume 129. London: William Heinemann, 1921.
^ab"Hercules, originally known as Engonasin, the Kneeler".Constellation Myths. Translated by Hard, Robin. Oxford University Press. 2015.ISBN9780191026539.
^Kunitzsch, P.; Smart, T. (2006).A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.).Cambridge,MA:Sky Pub. p. 35.ISBN978-1-931559-44-7.
