From time to time someone will ask me why I haven’t written about a specific topic. Since I usually write my column only once a month, I concentrate on astronomical events that any casual stargazer can observe. That includes annual meteor showers, the phases of the Moon, the bright planets, the northern lights, and any prominent sky phenomenon.
Occasionally I’ll highlight one of my favorite constellations. When I was recently asked to write about Hercules, I thought I had done so not long ago. Was I wrong! It has been several years. Somewhere along the line as I have gotten older, the passage of time has followed some perverse inverse square law – the older I get the faster time passes.
So for all of you who regularly read this column, I present one of those constellations which contains a magnificent astronomical object which can lure me out into the often murky, mosquito-infested skies of summer: Hercules.
Did the title of this article catch your eye? Did it seem familiar somehow? The sci-fi gurus among you will quickly recognize the title quote as exclaimed by David Bowman as he enters the “stargate” in 2001: A Space Odyssey. A similar psychedelic slit-scan effect was used during the early 70’s for the Doctor Who series opening title sequence. Though the object I love to examine does not display any of the motion the above mentioned special effects do, it is definitely “full of stars,” hundreds of thousands of stars!
I’m referring to the showpiece of northern hemisphere globular clusters, M13 in Hercules (so called for being the 13th entry in the sky catalog of 18th century astronomer Charles Messier). Before I describe this beautiful cluster of stars, let’s examine the Hercules star pattern. It has a wealth of mythology associated with it.
The origins of this constellation “giant” remain shrouded in the dim recesses of mankind’s past. The fact that this particular pattern of stars has always represented a giant lends credence to the idea that its form has remained unchanged for perhaps thousands of years. In this scenario, different cultures merely borrowed the form and tailored it to their own circumstances. The “kneeling one,” as the ancient Greek astronomers knew him, has come to us now in the form of Hercules.
Let’s examine the myth behind the man. Hercules was the son of the god Jupiter and a mortal woman, Alcmene. This union gave Hercules superior strength and other powers mortals did not possess. He was first put to the test as a child when he strangled some snakes the goddess Juno had sent to destroy him. You see, Juno was Jupiter’s wife, and she was fed up with the philandering of her husband with mortal women.
As a young man, Hercules’ strength and courage were both fully tested by King Eurystheus to whom Hercules owed allegiance. The king was jealous of Hercules fame as a hero, so he imposed twelve labors upon him. The king really wanted Hercules out of the way, since any one of the twelve tasks could have easily killed him. To make a long story short, Hercules succeeded in all the tasks, elevating him to even higher hero status.
However, Hercules’ ascension to the starry heavens is a tragic one. One day, as Hercules was about to set out on a journey, his wife Deianira presented him with a cloak. Unfortunately, she had received it as a gift from the dying centaur Nessus, whom Hercules had slain. The cloak was poisoned with the centaur’s blood. Hercules knew his undignified death was at hand, so he built a funeral pyre on Mount Etna, placed himself upon it, and set it afire. The poet Ovid, in his “Metamorphoses,” described what transpired next:
... Almighty Jove
In his swift car his honour’d offspring drove;
High o’er the hollow clouds the coursers fly,
And lodge the hero in the starry sky.
In today’s sky we find the mighty Hercules, kneeling upon the head of Draco the Dragon, holding a club in one hand, and a branch in the other.
Now that we know a little about the mythology of Hercules, where can one find this constellation giant? On an early June evening Hercules can be found about halfway up in the eastern sky at around 9:00 pm. Four main stars, called the keystone, outline the body of Hercules, while two streams of stars form his arms and another stream comprise his legs. Though his extremities look like a stick figure, Hercules has been bulking up on his body. Please see the accompanying star map.
What makes the pattern a little difficult to recognize is that Hercules rises on his side, with his head facing south (right). And, to make matters worse, when Hercules passes directly overhead later in the evening, he hangs upside down in our heavens.
Once you’ve located Hercules, there is one grand object you should hunt for. It is a globular cluster of stars that is visible to the naked eye in a dark sky. This cluster was discovered by Edmund Halley in 1714. Though thought to be a nebula, it is the showpiece of northern hemisphere globular clusters.
To find this magnificent cluster of stars please reference the star map once again. M13 is between the two stars that form the western side of the keystone. It is about 1/3 of the way from the northern most star of the keystone. Try locating it using a pair of binoculars. It looks like a tail-less comet.
Once you’ve found it, use a telescope if you have one. A small refractor will show it as a small diffuse patch of light, much like the nucleus of a comet. Larger scopes, say a four- or six-inch reflector, will begin to resolve individual stars within this beautiful beehive of stars. And the beehive description is quite apt, for if one could speed up time you would see these stars, which are all gravitationally bound to the cluster and number about 300,000, “orbit” the cluster like bees around a hive.
One of my favorite turn of the 20th century authors is Garrett P. Serviss. I often quote him in my columns because he had such a descriptive and poetic style of writing. For your enjoyment I have excerpted two quotes concerning M13 from his wonderful book, Pleasures of the Telescope.
“...smaller instruments reveal only the in-running streams and the sprinkling of stellar points over the main aggregation, which cause it to sparkle like a cloud of diamond dust transfused with sunbeams.” “It is a ball of suns. Now you need a telescope. You must have one. You must either buy or borrow it, or you must pay a visit to an observatory, for this is a thing that no intelligent human being in these days can afford not to see. Can it be possible that any man can know that fifteen thousand suns are to be seen, burning in a compact globular cluster, and not long to regard them with his own eyes?”
Furthermore, another popularizer of astronomy, Mary Proctor, in her 1925 edition of Evenings with the Stars, best summed up my initial thoughts about this beautiful cluster of suns saying, “The cluster is a mass of glittering starlight, each star a sun pouring forth supplies of light and heat, and all the electric and chemic influences which are as necessary as light and heat for the welfare of living beings — if any exist — on planets circling around these orbs ... If such worlds in space are a reality, and if they are inhabited by reasoning beings like ourselves, it is a fascinating idea to imagine what must be the appearance of the sky to dwellers on a planet circling around one of the stars in the centre of such a cluster as 13 Messier.”
On the next clear and moonless night, go out and locate the great Hercules in the sky. Binoculars will certainly show you M13, but a telescope will reveal all its splendor. Think about the above descriptions while you enjoy the image. Serviss and Proctor both had a way with words. Also remember Bowman’s exclamation. You may not enter a stargate, but starlight can certainly provide you with a trip through the universe.
And don’t forget that the local observatories are always “full of stars,” providing the skies are cloud-free. On the next clear Saturday night take a ride out to Seagrave Observatory (http:/www.theskyscrapers.org) in North Scituate. Or, on the next clear Tuesday night stop by Ladd Observatory (http://www.brown.edu/Departments/Physics/Ladd/) in Providence. Check out their websites for the public night schedules and opening times.
Keep in mind we can’t begin to observe the stars until around 9:30 pm the closer we get to the summer solstice.
Until next month, keep your eyes to the skies.