Constellation named after famous hero


By Tom Burns - Stargazing



The constellation Hercules rises in the east just after dark. Here’s how to find it.

After evening twilight, look directly overhead for a large trapezoid of stars called the Keystone, which makes up the trunk of Hercules’ body. His upraised arms stretch south, and his legs are to the north.

The constellation was so important to the ancients that they identified it with their greatest hero, called Heracles by the Greeks, about whom more myths developed than any other figure.

Oddly, Hercules is also one of the faintest constellations known to the ancients. These days, the great hero is washed away by the lights from the city.

You’ll need at least suburban skies to spot him. Stargazers can still see him pretty well at Perkins Observatory in Delaware. However, given the growth of Columbus street lighting and arena light beams, his prognosis is not good.

Legends about his exploits go back farther than history records. The earliest Greek stargazers called him Engonasin, the “Kneeling Man.” As he kneels, he places his left foot on the head of the giant dragon Draco, who stretches below him in the northern sky.

To later Greek and Roman writers, the stars represented the highest ideals of bravery and headstrong heroism and the lowest depths of insanity and depravity.

Things started badly for Heracles. His misfortune began with the first instant of his life. He was born out of the dalliance of Zeus, the king of the gods, and a human woman named Alcmene.

Zeus’ wife, Hera, was furiously jealous of Zeus’ many mortal lovers and their offspring, but there wasn’t much she could do to get revenge against her more powerful husband.

Instead, she took it out on the mortals. Hera had a grudge against Heracles from his birth, and he had to face her considerable wrath his entire life.

When he was still in his crib, Hera sent a couple of serpents to wring the life out of him. Such was his physical strength that, even as a baby, Heracles squeezed the life out of the snakes instead.

Heracles grew to a man with the physical strength of a god and all the weaknesses that an onerous mortal life can engender. In a fit of madness visited upon him by Hera’s evil spell, he murdered his children.

When sanity returned, the remorseful hero went to the Oracle at Delphi to beg for atonement. The Oracle ordered him to serve Eurystheus, King of Mycenae, for one year. At the insistence of Hera, Eurystheus ordered the hero to embark on his famous twelve labors.

The night sky is littered with the carcasses of the fantastical beasts that Heracles killed during his adventures. His bloody presence is felt all over the sky.

Among his famous labors, he killed the Lernean Hydra, visible as a long string of stars low in the southern spring sky. He also killed the Nemean Lion, which is said to be the constellation Leo, now sinking lower in the western sky.

Just below Leo in the southern sky is Cancer, the giant Crab, slain by Hercules as he battled the Hydra. The Crab and the Hydra were the nasty household pets of Hera. She sent them to bedevil humanity in general and Heracles in specific.

Released from his labors, Heracles tried to make a life for himself. He married the young and beautiful Deianeira, daughter of a king.

While traveling together, the couple came upon the centaur Nessus. Inflamed by her beauty, Nessus tried to ravish Deianeira. However, Hercules shot him with an arrow dipped in the poisoned blood of the Hydra he had killed earlier in his career.

The dying centaur offered Deianeira some of his poisoned blood. He falsely claimed that it would act as a love potion.

Later, when Deianeira wrongfully suspected Heracles of infidelity, she gave him a shirt dipped in the poisoned blood. It burned his flesh to the bone, and Heracles died a horrible death.

In agony, he built a funeral pyre for himself. His mortal part burned up in the flame. His immortal part rose into the sky, where he joined the gods. We see him there as the constellation Hercules to this very day.

That constellation has the privilege of containing the most beautiful astronomical object in our northern sky, the Great Globular Star Cluster, called M13 by experienced stargazers.

Finding M13 is easy enough once you find Hercules. Find the two stars on the west side of the Keystone. About 1/3 of the way down from the top star, you will see a small, fuzzy, round patch in binoculars, marked as M13 on the star chart.

The ancients must have seen it easily as a circular fuzzy patch. Even with today’s light pollution, it is visible to the naked eye from dark, rural sites.

Words fail me here. M13 is a tremendous sight in a telescope. If you go to a public stargazing session this summer, find the largest telescope on the field and ask the operator to point it at M13.

It contains perhaps a million stars, but you won’t see them all, even in a large telescope. Depending on the size of your telescope, you will see thousands or even tens of thousands of stars in one field of view, an explosion of starlight so dense that it is difficult to resolve the stars into individual points of light except in larger telescopes.

It looks like a globe of stars, dense with countless points of light at the center and slowly becoming more sparse as you move outward —a giant swarm of fireflies or a pile of diamond dust against the velvet blackness of the sky.

“Globulars” are clusters of stars that huddle around the dense galactic core but outside the galaxy’s primary disk. At about 22,200 light-years away from Earth, M13 is definitely out in the galactic suburbs. (One light-year is about six trillion miles.)

M13 is perhaps 145 light-years, over 850 trillion miles, in diameter.

In that relatively tiny space are crammed hundreds of thousands of stars. The average distance from one star to another in our section of the Milky Way is about seven light-years. At the dense core of M13, the stars are closer than one light-year from each other.

Like all star clusters, M13 was born out of a giant cloud of hydrogen gas. As the stars condensed from the cloud ten or so billion years ago, they used up virtually all of the available hydrogen.

Since its beginning, very few new stars have been born. No hydrogen remains to form new stars today.

Many of the stars in M13 have reached old age and will die in a billion or two years. Slowly, M13 will fade from view as its old stars die and no new stars are born to replace them. Better check it out now before it’s too late.

It is strange to imagine what it would be like to live on a planet orbiting one of those stars near the cluster’s center. The nighttime sky would be glorious, so filled with stars that it might even seem like daytime.

There would be so many stars that stargazers could never see past his immediate stellar neighborhood. They might never guess they were part of a giant galaxy in a universe of trillions of galaxies.

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By Tom Burns

Stargazing

Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.