Hercules and the Harp

© 2001 by Robert C. Moler

As far as I know Hercules never played the harp. But Lyra the harp is the constellation just east of the mighty hero in the sky. So I'll group them together for this article.

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It seems a gross injustice that the greatest hero of Greek mythology should be given a dim constellation, while the mythological nobody Orion gets the most famous constellation of all. However each has deep sky objects which are the best of their class. More on that later. Hercules is a Greek hero, but we know him by his Latin name. His Greek name is Heracles.

Hercules can be spotted by finding its central figure, that of a keystone. A keystone, for the architecturally challenged, is the trapezoid shaped stone at the top of an arch, that holds the whole thing up. The Keystone is an asterism, or informal constellation, like the Big Dipper, Summer Triangle, or the Great Square of Pegasus.

From the corner stars of the Keystone extend lines of stars that delineate the hero. As depicted in the sky, Hercules appears upside down. The lower part of his torso is the Keystone. His shoulders and an arm are seen to the south. And his head is Ras Algethi, which means "Head of the Kneeler". In pictures Hercules is generally seen on one knee.

The most fabulous sight in Hercules is M13, the Great Hercules Globular Star Cluster, which is seen along the western edge of the Keystone. Barely resolvable in a 6 inch diameter telescope, it is a breathtaking sight in larger telescopes. Globular star clusters contain tens of thousands of stars crammed into, well, a big glob maybe a 100 light years in diameter. M13 (Number 13 on Charles Messier's list of fuzzy objects that weren't comets.) is the finest globular visible in the northern hemisphere of the sky. M92 is another globular in Hercules, though more challenging to resolve than M13.

The star Ras Algethi is an interesting double star. It's two components are quite close, only 4.6 seconds of arc apart. They make an interesting color contrast. The brighter is orange, while the fainter is green or blue-green. Try your luck with it, I can't see any green in the dimmer star.


According to Greek mythology the harp was invented by the god Hermes (the Roman Mercury). who stretched strings across a tortoise shell. He gave it to his half brother Apollo, who in turn gave it to Orpheus. Orpheus played the harp so sweetly, he could soothe savage beasts and even move inanimate objects.

Lyra is small, but easily found. Its brightest star is Vega, the brightest star of the summer triangle and the 5th brightest star in the night sky. It is a calibration star, pure white spectral class A0, and magnitude 0.0. In calibrating the IRAS (Infrared Astronomy satellite) back in 1983, it was found that Vega gave off excess infrared radiation. Apparently it has a disk of material orbiting it. Perhaps a solar system in the making. The name comes from a phrase that means either "Falling Eagle " or "Falling Vulture". Owners of the ill fated car of the same name may prefer the latter translation. The rest of the constellation is a slender parallelogram of four stars.

The greatest telescopic wonder of Lyra is M57, better known as the Ring Nebula. Visible in most any telescope, it is not visible in any telescopic finder I've ever looked through. So I put the crosshairs at a point directly center between the two stars at the southern end of the parallelogram. M57 is a planetary nebula. Planetaries are called that because many look like Uranus and Neptune in telescopes. It is the gasses blown off a dying star that still dimly glows in its center. Astronomers pretty well agree that the true form of it is a smoke ring. There's a lesson in there somewhere.

About a degree north of the Ring is a faint blue and gold double star, a dimmer version of the famous double Alberio. It's catalogued as OS525.

Another grand telescopic object in Lyra is the star e (Epsilon) Lyrae. It can be seen in the binocular field with Vega as a double of equally bright stars. In a telescope with more power each can be split into two stars again. This is the reason that epsilon Lyrae is called the double-double star. One of the stars used to find the Ring Nebula is b (beta) Lyrae. It is an eclipsing binary star with a period of 13 days, varying from 3.4 to 4.1 magnitude. There is also a secondary minimum to 3.7 magnitude, half way between the primary minima. This star can be studied without a telescope. The last deep sky object in Lyra I'll mention is M56. Like most globular clusters, M56 takes a telescope of large aperture to resolve. Hercules and Lyra are that constellations that are the gateway to the wonders of the summer skies to the east and south, and hang around into autumn. .

Questions? Send Email to me at bob@bjmoler.org

Uploaded: 07/02/2001