For the week including June 11, 2010

Hoag's Object Hoag's Object Location Seyfert’s Sextet Seyfert's Sextet Location M5 M5 Location Larger Illustration

SERPENS, THE SNAKE

If you look toward the southeast after sunset, you will see the large constellation of Ophiuchus, the Serpent Bearer, spread across the horizon. Ophiuchus is an age-old constellation of the Greeks. It represents Asclepius, a son of Apollo, who invented medicine. Serpens, the snake he holds in his arms, is a symbol of restored life. At the time, snakes were thought to renew their lives whenever they shed their skins. The constellation of Serpens, the Snake, is the only one that crosses another and has two sections, Caput, the Head, and Cauda, the Tail.

Serpens is also home to one of the most beautiful globular clusters visible in the northern skies, M5. Globular clusters are spherically shaped groups of old stars that can contain anywhere from tens of thousands to several million stars. These vast orbs of stars, located beyond the plane of our galaxy, evolved from gases and material left over from the formation of our galaxy. One of the brightest in the sky, M5 is some 13 billion years old and its diameter is about 130 light years across, making it one of the oldest and largest clusters known. Shown in the photograph at lower left, M5 is fairly easy to find with binoculars and makes quite a sight for the amateur astronomer.

The upper left photograph shows Seyfert’s Sextet, a cluster of distant galaxies named for the American astronomer, Carl K. Seyfert. These galaxies are so close together that their mutual gravitational attractions are causing collisions and mergers. Studies of Seyfert’s Sextet have revealed a great deal of information about the effects of gravity on the formation and structure of galaxies. In fact, the upper-left member of the group may only be a tidal distortion of one of the other galaxies and not a true galaxy on its own. For those with a good backyard telescope, Seyfert’s Sextet is a great addition to an amateur observer’s log.

Ring galaxies form from the collision of a large massive galaxy with a smaller one. Depending on the speeds and angles at which the galaxies are moving, the smaller galaxy can have its stars strewn around the outside of the larger creating a Saturn-like halo.

A fine example of a ring galaxy is Hoag’s Object, shown at upper right. Hoag’s Object consists of an elliptical galaxy surrounded by a loop of bright young stars. Elliptical galaxies are so dense with stars that they appear in telescopes as featureless glowing orbs. They most commonly originate through the mutual absorption of several large galaxies. The bright star ring is the remains of yet another galaxy that was not fully drawn into the core. Hoag’s Object is slightly larger than our Milky Way and these galaxies may have something more in common than just size. Astronomers at New Mexico’s Apache Point Observatory have announced the discovery of a great number of old stars arrayed in an arc just beyond the rim of our galaxy. Their report echoes the findings of astronomers from the University of Groningen who found a similar arc of stars while exploring an entirely different region of the galaxy. Together their results indicate that our Milky Way may be a ring galaxy too.

The photographs of M5, Seyfert’s Sextet and Hoag's Object are from the Hubble Space Telescope.

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