Hercules

Hercules

Constellation
List of stars in Hercules
Abbreviation	Her
Genitive	Herculis
Pronunciation	/ˈhɜrkjʊliːz/, genitive /ˈhɜrkjʊlɨs/
Symbolism	Heracles
Right ascension	17
Declination	+30
Area	1225 sq. deg. (5th)
Main stars	14, 22
Bayer/Flamsteed stars	106
Stars with known planets	7
Bright stars	0
Nearby stars	4
Brightest star	β Her (2.8m)
Nearest star	GJ 661 (20.9 ly)
Messier objects	2
Meteor showers	Tau Herculids
Bordering constellations	Draco Boötes Corona Borealis Serpens Caput Ophiuchus Aquila Sagitta Vulpecula Lyra
Visible at latitudes between +90° and −50°. Best visible at 21:00 (9 p.m.) during the month of July.

Hercules is a constellation. It is named after Hercules, the Roman mythological hero adapted from the Greek hero Heracles. Hercules was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations today. It is the fifth largest of the modern constellations.

History

The constellation was not always identified with Heracles/Hercules. In earlier times, for example in the Rudolphine Tables, an alternative Greek name was Engonasin, meaning "on his knees" or "the Kneeler".

Notable features

Stars

Hercules has no first magnitude stars.

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, is located within Hercules, close to Vega in neighboring Lyra.

Planetary systems

Seven stars in Hercules are known to be orbited by extrasolar planets. They were discovered in 1996, 2005, two in 2006, and three in 2007.

• 14 Her has one confirmed and one unconfirmed planet. The planet 14 Her b was the longest period (4.9 years) and widest orbit (2.8 AU) at the time of discovery. The planet 14 Herculis c orbits much further out with very low eccentricity

• HD 149026 has a transiting hot Jupiter planet and is one of the most prominent and studied.

• HD 154345 has the planet HD 154345 b, a longest period (10900 days) and widest orbit (9.21 AU) of any planets other than imaging planets.

• HD 164922 has the first long period Saturian planet discovered. The mass is 0.36 M_J and semimajor axis of 2.11 AU.

• HD 147506 has the most massive transiting planet HAT-P-2b at the time of discovery. 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.

• GSC 03089-00929 has a short transiting planet TrES-3. The period was 31 hours and undergoing orbital decay.

Deep sky objects

Hercules contains two of the most conspicuous globular clusters: M13, the brightest globular cluster in the northern hemisphere, and M92. It also contains the nearly spherical planetary nebula Abell 39. M13 lies between the stars η Her and ζ Her; it is dim, but may be detected by the non-aided eye on a very clear night.

Visualizations

Hercules as depicted in Urania's Mirror, a set of constellation cards published in London c.1825. The figure appears upside down in the sky relative to neighbouring constellations.

An alternative way to connect the stars of the constellation Hercules, suggested by H.A. Rey. Here, Hercules is shown with his head at the top.

The traditional orientation visualizes α Herculis as Hercules's head; its name, Ras Algethi literally means "head of the kneeling one." The left hand then points towards Lyra from his shoulder (Delta Herculis), and Beta Herculis forms his other shoulder. His narrow waist is formed by Epsilon and Zeta Herculis. Finally, his left leg (with Theta as the knee and Iota the foot) is stepping on Draco's head, the dragon/snake who Hercules has vanquished and perpetually gloats over for eternities.

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 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 (Gemma, or Alphecca) in the constellation Corona Borealis. The hero's right leg contains two bright stars of the third magnitude: α Her (Ras Algethi) 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.

References

• H.A. Rey, The Stars — A New Way To See Them. Enlarged World-Wide Edition. Houghton Mifflin, Boston, 1997. ISBN 0-395-24830-2.
• Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London. ISBN 978-0007251209. Princeton University Press, Princeton. ISBN 978-0691135564.

External links

Wikimedia Commons has media related to: Hercules (constellation)

• The Deep Photographic Guide to the Constellations: Hercules
• The clickable Hercules
• Star Tales – Hercules

Coordinates: 17^h 00^m 00^s, +30° 00′ 00″