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THE PERFECT SPHERE

Right ascension 16h 27m 33.737s Declination +27° 54′ 33.44″! Distance 6.8 kly (2.1 kpc)[Apparent magnitude (V) Integrated: 13.7; ! Central Star: 15.5 ± 0.2 ! Apparent dimensions (V) 155″.1 × 154″.5! Abell 39 is a low surface brightness planetary nebula. Minimum requirements to detect it: 8-inch telescope, and very dark skies! It is the 39th entry in a catalog of large nebulae discovered by George Abell. It was discovered in 1966 as part of the Palomar Observatory Sky Survey. It has been expanding from the for about 22,100 years. Its greenish-bluish hue denotes a strong OIII emission. It is almost perfectly spherical in shape and one of the largest known spheres in the universe. It has a radius of about 2.5 light-years. It is estimated to be about 6,800 light-years from earth and 4,600 light-years above the Galactic plane The central star has a magnitude of 15.5. The star has an estimated temperature of 150,000K and a mass ~.6 solar masses. Precise measurements indicate that the central star is slightly off-centre, by about a tenth of a light year. The central star is distinctly blue-white in color. A blue-white color indicates that the central star (white dwarf) is very hot. It emits copious amounts of UV radiation which excite the surrounding gas and make it fluoresce its green- blue color. The butterfly-like shape of many nebulae, and filaments or clumps of dense gas within them, cause starlight to penetrate the nebulae unevenly, However, the nearly perfect spherical nature of Abell 39 allows astronomers to accurately estimate how much relative material is actually absorbing and emitting light. Abell is an important object of study because of this. Abell 39 is so faint that astronomers were unable to measure all the critical information from the nebula that is needed to isolate the cause of the composition measurement discrepancies, even though they used the National Science Foundation's Mayall 4-meter telescope at Kitt Peak National Observatory to collect spectral details. Instead, they provide their predictions of what they expected to measure, in order to guide future observers with more sensitive equipment and larger telescopes.

SON OF ZEUS, KILLER OF MONSTERS

Left: Representation of Hercules, taken from Uranographia by Johannes Hevelius, a star chart circa 1690 Constelllation of Hercules in Zenith - Photograph © Till Credner and Sven Kohle

THE GREAT GLOBULAR CLUSTER IN HERCULES

Man, God or Star-cluster? In Greek Mythology, Herakles was the result of a union between Zeus (the king of the Gods) and Alcmene (daughter to King Electryon, of Mycenae). A demigod, he was half mortal, possessing superhuman strength and martial prowess. In Roman Mythology his name was Latinised to Hercules, although the Latin Hercules was slightly different from the Greek figure. The Romans made a few additions and modifications to his persona, such the tale of Hercules defeating the monstrous Cacus (a fire breathing evil offspring of the God Vulcan), who lived in a cave under the Palatine Hill (one of the eventual Seven Hills of Rome). As an illegitimate son of Zeus he was despised by Hera, the wife of Zeus. Her attempts to destroy him led to a lifetime of toil and tragedy for the demigod. A few months after his birth, Hera sent two serpents to kill him. Herakles strangled the snakes in either hand and was found in his cot playing with the dead serpents, as if they were mere toys. This was the first in a series of challenges she would test him with. Herakles became a favorite with other gods. Apollo crafted his bow and arrows; Athene gifted him a magnificent robe; Hermes provided him with a sword, and Castor (the greatest warrior) taught him how to use it. Hephaestus, the blacksmith of the gods, made a golden breastplate for Herakles. Though often virtuous and heroic, he was also extremely passionate and quick to anger. A fast friend, and a monstrous enemy. In later life he did great and terrible deeds alike; killing many of his friends and loved ones in fits of insanity brought on by Hera's spite, and using his power to defeat evil and slay monsters and beasts. He also killed who got in his way or offended his keen sense of honor. In this sense he was not a purely virtuous hero, and was just as capricious as the Gods from which he descended. He is probably best known for his Twelve Labours. Driven insane by Hera, he killed his children from his marriage to Megara, queen of Thebes. Disgraced, Hercules' penance was set by Eurystheus, Hercules' enemy who had taken Hercules' place as King in light of the Hero’s disgrace. He was tasked to complete 10 nearly impossible trials. That he completed all 10 meant 2 more were added afterwards, in attempt to foil him. Unsurprisingly, Hercules aced these as well. These labours, in the chronological order given by the writer Apollodorus were; 1st. Kill the Nemean lion, 2nd. Destroy the Lernaean Hydra. 3rd. Capture the Ceryneian Hind. 4th. Capture the Erymanthian Boar 5th. Clean the Augean Stables. 6th. Kill the Stymphalian Birds. 7th. Capture the Cretan Bull. 8th. Round up the Mares of Diomedes. 9th. Steal the Girdle of Hippolyte. 10th. Herd the Cattle of Geryon. 11th. Fetch the Apples of Hesperides. 12th. Capture Cerberus. In further adventures, he voyaged with the Argonauts, freed Prometheus from his chains, founded the domain of Scythia, married four times, had countless lovers of both genders and challenged the God Dionysus to a drinking contest (which Hercules lost!) His eventual death was caused by the trickery of Nessus, a Centaur. He was deceived (inadvertently by his current wife Deianara). Told by the dying centaur that a garment stained in deadly Hydra blood would excite the love of her husband, Hercules was later made to wear the garment in an ill advised moment of passion. This was the end of him. Instead of the agonizing slow death of the poison, Hercules chose instead to immolate himself on a funeral pyre made of trees he himself had uprooted, as the Hydra's venom boiled the skin from his bones. As his mortal body burnt away, his immortal self rose to Olympus, and he was deified, to live eternally among the Olympians.

Above: Main star grouping within the Hercules constellation His two most famous motifs are perhaps the massive wooden club he wielded and the skin of the Nemean lion he wore as a cloak. In the constellation, located between Lyra and Bootes he is seen wielding his club, with his foot on the head of Draco the Dragon. Like the man himself, the constellation is huge, the fifth largest in the sky. The crouching man also has violent mythological relationships with other constellations in the comos! Cancer: The Latin for Cancer means Crab, and in Greek mythology the crab was sent to distract Hercules when he was fighting with the monster Hydra. Hercules crushed the crab under his foot, and as a reward for its sacrifice, Hera (wife of Zeus), placed it among the stars. Leo: Represents the Nemean Lion, unfortunate enough to be the victim of one of Hercules' labours. The lion found its way to the heavens to commemorate the great battle with Hercules. Draco: Draco represents Ladon, the dragon sometimes depicted with one hundred heads; who guarded the sacred spring where the golden apples of the Hesperides were found. Draco was defeated as part of our Hero’s 11th labour.

“A buffoonish Hercules comes to the house of his friend Admetus…Hercules overindulges, as usual.” – Euripides, Alcestis

17h 17m 07.27s! Declination: !+43° 08′ 11.5″[1]! Distance: ! 26 kly (8 kpc)! Apparent magnitude (V) ! +6.3! Apparent dimensions (V): ! 14' arc minutes! It is located nine degrees northeast of M13, and six degrees directly north of pi Herculis. lying only 9.5 degrees northeast of the spectacular globular cluster M13, it is often overlooked in favour of it's more spectacular cousin. It shines with the light of 250,000 Suns from a distance of about 35,000 light years. It was first discovered by Johann Elert Bode in 1777. He remarked; "A nebula. More or less round with pale glow. On this occasion, I also want to announce that on December 27, 1777 I have discovered a new nebula in Hercules, not known to me..” It was later independently rediscovered by Charles Messier on March 18, 1781 who commented that it "...resembles the nucleus of a large Comet” M92 is at a distance around 26,000 light-years away from Earth. It may have a mass of up to 330,000 suns. It is visible to the naked eye under very good conditions. M92 makes a triangle with the two northernmost stars in the keystone. It could be imagined as where Hercules' head would be. It is a Class IV globular on the Shapley-Sawyer scale, which ranges from I, for highly concentrated clusters, to XII for the least concentrated The precession of Earth's axis will cause M92 to become our "North Cluster" or "Polarissima Borealis" in about 14,000 years, as it was previously, about 12,000 years ago. M 92 has a reputation as being among the oldest of globular clusters, and is also one of the most metal poor, its iron content well under one percent.

M92 is approaching us at 112 km/sec. Its fainter stars can be seen when “averted vision” is used - just look slightly away from the centre of the cluster!

Is located in the 'armpit' of the Hercules constellation. M13 lies on a line between eta Herculis and zeta Herculis, due west of pi Herculis. It is one of the best known clusters in the northern hemisphere. which vies with M5 in Serpens for the title of visually brightest in the northern hemisphere. It is barely visible with the naked eye on a very clear night. It is a Class V globular cluster. M13 was discovered by Edmond Halley in 1714, and catalogued by Charles Messier on June 1, 1764. Edmond Halley wrote in his notes (in the fantastic language of the time) upon discovering the cluster: "This is but a little patch, but it shews it self to the naked Eye, when the Sky is serene and the Moon absent." Welsh amateur astronomer Isaac Roberts is believed to have taken the first published photograph of M13 on May 22, 1887 (a sixty minute black and white photograph taken with a 20-inch reflector). Many of the stars in M13 are extreme Population II stars that are poor in heavy metals, and were formed 12 billion years ago. It is about 145 light-years in diameter, and is composed of several hundred thousand stars. Look in the southeast corner to see "the Propeller", a Y-shaped area devoid of bright stars The brightest star in M13 is the variable star V11. The reason for the low abundance of unusual blue straggler stars in M13 is currently unknown. if you made a scale model of M13 where the stars are the size of a grain of sand, the grains of sand would be separated from each other nearly a mile, even in the closely packed center of the cluster The Arecibo Message of 1974, designed to communicate the existence of human life to hypothetical extraterrestrials, was transmitted toward M13. However, due to the large distances involved, M13 will no longer be in that location when the radio message finally arrives, around 25,000 years from now. The center of M13 is roughly 500X more concentrated than its outer perimeters. It has a lot of stars at its core! In The Sirens of Titan, Kurt Vonnegut wrote "Every passing hour brings the Solar System forty-three thousand miles closer to Globular Cluster M13 in Hercules -- and still there are some misfits who insist that there is no such thing as progress."

Many cultures have associated Hercules with the heroic archetype, doing battle with Draco. He is particularly well described in Mesoptamia, from where the Greeks would later obtain much of their science, mythology and cultural references.

When not hunting down other constellations, Hercules’ plays host to a plethora of stars, meteoric activity and exotic deep sky objects.

A ‘LESSER’ GLOBULAR CLUSTER??

GB

The legend and mythology of Hercules has endured (with some changes) in our modern popular culture

Taken from Moore, P., 2002. Philip's Astronomy Encyclopedia Fully rev. and expanded ed., London: Philip's.

Right ascension: !

Right ascension 16h 41m 41.44s ! Declination +36° 27′ 36.9″ ! Distance 25.1 kly ! Apparent magnitude (V) +5.8 ! Apparent dimensions (V) 20 arcmins!

in Babylon he was seen as the kneeling man. In their mythology it was represented as the heroic demigod, Gilgamesh, who was the main character in the Babylonian Genesis. Gilgamesh stood on the head of the dragon (the constellation Draco) in the north. Interestingly, the Bible bears many resemblances to Gilgamesh’s story (the Babylonian story predates the bible by at least 1500 years) . The Epic of Gilgamesh includes a world-wide flood, a fruit from a tree that grants great power (Eden?) and a hero who is of partly-divine descent (the Nephilim of Genesis?)

Stars in Hercules α Herculis (Ras Algethi, kneeler's head) is a red super-giant star about 600 times the Sun's diameter. Like most red giants it is an erratic variable fluctuating between magnitudes 3 and 4. It is actually a double star with a magnitude 5.4 blue-green companion, visible in small telescopes.

The Phoenicians called Hercules Melkarth or Melqart, after one of their gods (one of the stars, mu Her, is still called Melkarth). The astronomer priests of the Euphrates valley associated Hercules with their sun god. Melqart was often depicted as a bearded figure, wearing a high, rounded hat, a kilt and holding an Egyptian ankh, the symbol of life. Under the name Malku he was equated with the Babylonian Nergal, god of the underworld and death. In Assyrian sources, Hercules was known as lzdubar or Gisdubar and written of in texts from 3000 BC. At that time he was connected with Sun worship. Another heroic slayer of beasts, born the son of a king in Ourouk, he was cast out of his Kingdom to live in the wilderness. Speaking of his exploits to his mother he says in prophetic speech; "I have dreamed a dream; the stars rained from heaven upon me; then a creature, fierce-faced and taloned like a lion, rose up against me, and I smote and slew him." This epic poem is a relatively recent find in the west, having been discovered in 1871 by the Assyriologist, George Smith.

β Her (Kornephoros) is a magnitude 3.8 white star 140 light years away. It consists of a close pair of stars orbiting one another in about 14 months. A wide 10th magnitude companion is probably not connected with the other two stars. γ Her is a magnitude 3.7 star nearly 200 light years away. It has a 9.9 magnitude companion 42" from it. δ Her (Sarin) is a magnitude 3.1 white star 91 light years away. Small telescopes show a magnitude 8.8 star nearby, which is physically unrelated, making this a fine example of an optical double. ζ Her is a magnitude 3.1 white star 31 light years away, with a close magnitude 5.6 red companion orbiting the primary every 34.5 years. The stars are closest in 2001, but were widest in 1990. Since William Herschel first measured the binary star, more than six complete revolutions have taken place. κ Her (Marfak) is a magnitude 5.0 yellow giant with a magnitude 6.3 companion easily seen in small telescopes. The pair lie about 280 light years away. ρ Her is a blue-white magnitude 4.5 star with a magnitude 5.5 companion lying 170 light years away. This is a fine binary for small apertures. The primary is a very close interferometric pair McA 48. 95 Her is a famous pair of stars lying 470 light years away, suitable for small telescopes. A great many double star observers in the 19th Century estimated the colours from "apple green and cherry red" of Piazzi Smith to both pure white. Colour estimates with older refracting telescopes were rather unreliable and the stars appear pale and deep yellow.

Precise analysis of a high-resolution image of Schwassmann-Wachmann 3 (SW3) taken in May 2006 by the Subaru Telescope. It reveals that one chunk called Fragment B is split into at least 50 fragments. This is well more than the 13 estimated when the image was first released in 2006

Celestial Showers in Hercules From May, 19th, to June 19th, the meteor shower Tau Herculids becomes active. On June, 9th, the maximum occurs with about 4 meteors. The parent comet of the Tau Herculids is Schwassmann-Wachmann 3. The meteor shower was first observed in May 1930, by the Kwasan Observatory in Kyoto, Japan. Hercules X-1 Hercules X-1 (Her X-1), also known as 4U1656+35, is a moderately strong X-ray binary source discovered in 1973. It is composed of a rapidly rotating neutron star accreting matter from a 'normal' star (HZ Her) As it rips matter away from it’s larger partner, the pulsar gives off X Rays. The spectrum of Hercules X1 shows a periodicity of 1.2378 sec; this is the time it takes for the pulsar to complete one spin. This is a common value for pulsars . Every 1.7 days the signals stop. This is probably caused by X1’s larger companion obscuring the X ray pulse. The system lies in a distance of about 20000 lightyears from us. X1’s mass has been determined to be 0.9 +/- 0.4 solar masses.

95 Her is a pair of 5th magnitude stars with a separation of 6.3". They were first measured by F Struve in 1829. During the 19th century there were reports of fluctuating colours, but now they are seen as an identical coloured yellow pair.

1. Planetary Nebula: Are formed as a consequence of the actions of a gravitationally unstable giant star, in the later stages of its life. The nebula itself is made up of an expanding shell of ionized gas and plasma that once formed the star's outer layers, this shell is pushed outwards by the energetic solar wind and magnetic pulses of the star. Though not directly related to planets, the term planetary nebulae was coined in the 18th century because of the resemblance of these objects to planets, when seen through a low quality telescope. This was before the exact nature of planetary nebulae was known. Other famous examples include the Cat's Eye Nebula and the Ring Nebula. These are often aptly named; many of these planetary nebulae bear striking resemblance to their individual namesakes. They are vitally important to the chemical evolution of the surrounding galaxies, creating heavier metals from elemental hydrogen and helium, and expelling them into space. 2. Globular Cluster: A gravitationally bound group of stars which have formed a spherical shape. The stars orbit a common centre of mass, and increase in density with proximity to the globular core. Though first observed in 1665 by Abraham Ihle, a German, it wasn't until Messier observed M4 in 1674 that individual stars were resolved within a globular. Such clusters are often found in the halo of a galaxy, made up of low metal, older stars. They are much older than open clusters,. There is very little free dust and gas in these systems, which is thought to have been taken up by the stars. Interestingly, due to the high volume of stars within these clusters, and complex gravitational interactions this causes, they are thought to be unfavorable areas for planetary formation. It is believed that there are around 170 in the Milky way (with some yet undiscovered) 3. Edmund Halley: Born in Shoreditch in 1656, Halley was an English astronomer and physicist. A prodigious child with an interest in mathematics, he was the son of a wealthy businessman. After graduating from Oxford University in 1676 he spent the rest of his life in the pursuit of knowledge. Amongst his many achievements include pioneering work on magnetic laws, attempts at scientifically dating Stonehenge, and studies of motions in the earth's atmosphere. In 1720 he was made the Astronomer Royal. He is perhaps best known for computing the orbit of Halley's comet and persuading Isaac Newton to publish Principia, which was vital to the advancement of physics. 4. Charles Messier: Born in Badonviller, Charles Messier was the 10th of 12 children and the son of a Court Usher. A self made man who worked his way up from humble beginnings, he started his astronomical career in 1751 in the employ of the astronomer of the French Navy. An extremely talented observer, and methodical in his note taking, in his prestigious career most of his discoveries where made on a 4 inch telescope, which are a testament to his abilities. His first documented observation was of the transit of Mercury in 1753. In 1770 he was made a fellow of the French Academy Of Sciences. Many of the objects in his catalogue where discovered by his assistant, Pierre Mechain. His database, published is still in use, however it has been somewhat superseded by the New General Catalogue. He died in his 87th year, at his home in Paris.

References Babe, G., 2007. BBC - h2g2 - Constellations: Hercules 'the Strongman'. BBC DNA. Available at: http://www.bbc.co.uk/dna/h2g2/A29778916 [Accessed April 19, 2010]. Cox, S., 2010. Observing M13 in the Constellation Hercules. HubPages.com. Available at: http://hubpages.com/hub/Obsreving-M13-in-the-Constellation-Hercules [Accessed April 19, 2010].

Stars in Hercules information Credited to Paul Rodmell - http://www.rasnz.org.nz/Stars/Hercules.htm

Isbell, D., 2001. Rare Spherical Planetary Nebula Provides Step Toward Accurate Measurement of Chemical Compositions in Stars. National Optical Astronomy Observatories News. Available at: http://www.noao.edu/outreach/press/pr01/pr0102.html [Accessed April 20, 2010]. Kaler, J., 2004. Heroic Stars. University Of Illinois. Available at: http://stars.astro.illinois.edu/sow/heroic.html [Accessed April 19, 2010]. Plotner, T., 2009. Messier 92. Universe Today. Available at: http://www.universetoday.com/guide-to-space/messier-objects/messier-92/ [Accessed April 19, 2010].

Artist’s impression of an X-ray binary system © Fahad Sulehria, www.novacelestia.com

Russell, A., Art Russell's Monthly Messier Star-Hop; September #2. Available at: http://education.gsu.edu/spehar/FOCUS/Astronomy/star-hop/Monthly/msh09-2.htm [Accessed April 19, 2010]. Smith, D., 2000. Hercules. dibonsmith.com. Available at: http://www.dibonsmith.com/her_con.htm [Accessed April 19, 2010]. Welton, S., 2009. Visual Astronomy: Constellation Showcase: Hercules. Visual Astronomy. Available at: http://www.visualastronomy.com/2009/07/constellation-showcase-hercules.html [Accessed April 19, 2010]. Whitehouse, D., 2001. BBC News | SCI/TECH | 'Soap bubble' space clue. BBC News. Available at: http://news.bbc.co.uk/2/hi/science/nature/1134888.stm [Accessed April 20, 2010]. Whitt, K., 2008. Observing the Stars of Hercules: The Constellation of the Strong Man. Suite101.com. Available at: http://stargazing.suite101.com/article.cfm/observing_the_stars_of_hercules [Accessed April 19, 2010].

Jack Oughton


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