Hercules the most famous of all the Greek Heroes. In mythology Hercules was the son of Zeus and his lover the mortal princess Alcmene. When Zeus’s wife Hera discovered Hercules was Zeus’s illegitimate son she drove him mad. Myth has it that Hercules then in his madness killed his wife and children.
Wanting to atone his crime Hercules consulted the Oracle at Delphi. He was commanded to serve his cousin, Eurystheus, King of the Kingdom of Argos for 12 years and he was given the 12 Labours of Hercules. The killing of the Lion Leo, slaying of the multithreaded Hydra and the dragon Ladon were a few of the labours. His final labour was to descend into the underworld and kill Cerberus the guardian of the gates of hell.
Hercules also was a voyageur on the Argo Navis with Jason in the search for the Golden Fleece.
Hercules fell victim to the poison of Hydra and in perpetual agony killed himself. He was placed in the sky amongst the stars by Zeus where with a lot of imagination and good dark skies we can see him near the horizon in our northern sky tonight.
The supernaturally strong demi-god is depicted in old drawings kneeling with his foot on the head of Draco the Dragon. He stands upright in our sky, which is unusual as most of the constellations were labelled and named in the Northern Hemisphere. This is because Hercules was first discovered in 1714 by Edmond Halley, the English scientist, who catalogued the stars of the southern hemisphere.
Hercules is the fifth largest constellation. It is a more popular constellation in the Northern Hemisphere than here in Australia where it never rises very high above the horizon. However it is worth a night of observing and now is the best time as this is the highest it will get in our skies. Hercules is found in the northern sky west of the bright 0.03 magnitude star Vega in Lyra.
Alpha Herculis, a red supergiant represents Hercules’ club, a variable of 3.0 – 4.0 mag. in 180 days. It is also a double with a blue-green 5.4 mag companion visible in small telescopes.
Beta Her. , 2.8 mag. yellow giant is the right shoulder of Hercules.
The Keystone the most distinct pattern of the faint constellation, marks the pelvis of Hercules and has four corner stars, Zeta ( ζ )mag 2.8 on south western corner, Epsilon ( ε ) mag 3.9 on the south eastern corner, 3.5 mag. Eta ( η) on the north western corner and mag. 3.1 Pi ( π ) on the north eastern corner.
The Great Hercules Cluster M13 (NGC 6205) is the most outstanding globular cluster in the Northern Hemisphere with a magnitude of 5.8 and apparent diameter of 20’ it spreads across 140ly and includes around 300,000 stars 23,500 ly away.
M13 lies on the western side of the central Keystone of four stars marking the pelvis of Hercules, approximately 2 ½ ° south of magnitude 3.5 Eta (η) Herculis. It is easily spotted in binoculars as a fuzzy ball and in dark skies will be visible to the naked eye.
In a small telescope the cluster has a condensed centre with gradual spreading out of light. With a larger telescope at higher power the stars can be more easily resolved (i.e. 105mm scope).
Also look for two 7th -magnitude stars bracketing the cluster when observed at low power.
Take time to compare M13 with our most brilliant globular cluster in the Southern Hemisphere the magnitude 3.7 Omega Centauri which lies only 17,000 ly away and 47 Tucana the 4th-magnitude brilliant globular cluster 15,000 ly away.
M92 (NGC 6341) is a 6.4 mag. globular cluster 25,500 ly away, visible with binoculars with an apparent diameter of 12’. Only 10 light years smaller than M13 it is only slightly less bright than M13, however being more condensed in the centre than M13 it requires a larger telescope to resolve its stars with approximately 72x to 130x magnification. It is located 5° south west of Iota (ι).
NGC 6210 is a brilliant but small 9th magnitude planetary nebula which appears as a blue-green ellipse in larger than 75mm telescopes. It is 4000 ly away. It is similar in appearance to the Eskimo Nebula in Gemini. NGC6210 forms a small triangle with two neighbouring stars 3° north east of Beta Herculis.
References: Collins Stars & Planets 2nd Edition, 1993; Myths & Legends of Greece & Rome, H A Guerber 1996; Hartung’s, Malin & Frew 1995; The Messier Objects, Stephen James O’Meara, 2000