A

David

Darling

Hercules

Hercules constellation

Figure 1. The constellation Hercules. © 2003 Torsten Bronger.


Hercules X-1

Figure 3. Artist's impression of Her X-1. Credit: D. Klochkov.


Hercules (aabreviation: Her), representing the mythical hero famed for his 12 labors, is a very large but unspectacular northern constellation. It contains the Keystone asterism, named after its shape, which is made by four of the main stars in Hercules – Epsilon, Zeta (Ruticulus), Eta, and Pi Her. See below for details of the constellation's brightest stars and interesting deep sky objects.

 


Hercules Cluster

 

Hercules Cluster (Abell 2151)
Figure 2. The Hercules Cluster.

 

The Hercules Cluster (Abell 2151) is a loose unsymmetrical cluster of about 75 bright galaxies, some 500 million light-years away and about 6 million light-years across (see Figure 2). It contains an unusually high proportion of spiral galaxies and also galaxies that shown evidence of interaction or other peculiar features (see galaxy interaction).

 


Hercules X-1

 

Hercules X-1 is an X-ray pulsar that is a member of an eclipsing binary system with an orbital period of 1.7 days; it lies about 15,000 light-years away. The visible component has been identified as the blue variable HZ Herculis, whose spectrum varies from late A or early F to B. Her X-l has a pulsation period of 1.2378 seconds, presumed to be its rotation period, and shows a 35-day quasi-periodicity in the X-ray region (but not in the optical). It is thought to move in a nearly circular orbit, to be accreting matter from HZ Her, and to have a mass of about 0.7 solar mass. The orbital period is stable, but the pulsation period is speeding up at a rate of about 1 part in 100,000 per year. The X-ray eclipse lasts 0.24 days.

 


Stars brighter than magnitude 4.0
Star< Visual mag. Abs. mag. Spectral type Distance (lt-yr) R.A. (h m s) Dec. (° ' ")
Beta (Kornephorus) 2.78 -0.50 G8IIIa 148 16 30 13 +21 29 22
Zeta (Rutilicus) 2.81 2.64 F9IV 35 16 41 17 +31 36 10
Alpha (Rasalgethi) 3.00 -0.02 M5Ib-II 382 17 14 39 +14 23 25
Delta (Sarin) 3.12 1.21 A3IV 79 17 15 02 +24 50 21
Pi 3.16 -2.10 K3IIab 367 17 15 03 +36 48 33
Mu 3.42 3.80 G5IV 27 17 46 27 +27 43 15
Nu 3.48 0.80 G8II 112 16 42 54 +38 55 20
Xi 3.70 0.20 G8III 163 17 57 46 +29 14 52
Gamma 3.70 0.61 K0III 135 16 21 55 +19 09 11
Iota 3.82 -2.09 B3V 495 17 39 28 +46 00 23
Omicron 3.84 -1.30 B9.5V 347 18 07 32 +28 45 45
109 3.85 0.87 K2.5IIIab 128 18 23 42 +21 46 11
Theta 3.86 -2.70 K1IIaCN 670 17 56 15 +37 15 02
Tau 3.91 -1.02 B5IV 315 16 19 44 +46 18 48
Epsilon 3.92 0.43 A0V 163 17 00 17 +30 55 35

 

Other objects of interest
Name Type of object Notes
NGC 6210 planetary nebula A bright inner ring surrounded by a faint outer ring. Magnitude 9.7; diameter 13 × 20" (inner), 20" × 43" (outer); R.A. 16h 44.5m, Dec. +23° 49'
Great Cluster in Hercules globular cluster M13 (NGC 6205). See separate entry
M92 (NGC 6341) globular cluster NGC 5139. See separate entry

 

Constellations
Andromeda | Antlia | Apus | Aquarius | Aquila | Ara | Aries | Auriga | Bootes | Caelum | Camelopardalis | Cancer | Canes Venatici | Canis Major | Canis Minor | Capricornus | Carina | Cassiopeia | Centaurus | Cepheus | Cetus | Chamaeleon | Circinus | Columba | Coma Berenices | Corona Austrina | Corona Borealis | Corvus | Crater | Crux | Cygnus | Delphinus | Dorado | Draco | Equuleus | Eridanus | Fornax | Gemini | Grus | Hercules | Horologium | Hydra | Hydrus | Indus | Lacerta | Leo | Leo Minor | Lepus | Libra | Lupus | Lynx | Lyra | Mensa | Microscopium | Monoceros | Musca | Norma | Octans | Ophiuchus | Orion | Pavo | Pegasus | Perseus | Phoenix | Pictor | Pisces | Piscis Austrinus | Puppis | Pyxis | Reticulum | Sagitta | Sagittarius | Scorpius | Sculptor | Scutum | Serpens | Sextans | Taurus | Telescopium | Triangulum | Triangulum Australe | Tucana | Ursa Major | Ursa Minor | Vela | Virgo | Volans | Vulpecula