Thursday, July 30, 2009

Gobs of Globs

Note: There will be no August 6 post so that I may prepare for a She Is An Astronomer outreach event. Enjoy the July 30 post or browse my older posts. I'll be back with a new post on August 13.

Last week we looked at a bright open cluster in the summer constellation Ophiuchus the Snake Handler. Now let’s look at a different type of star cluster of which Ophiuchus contains a plethora: the globular cluster.

Globular clusters, or “globs” as they are commonly known, are dense balls of gravitationally bound stars. There are at least 150 known globs in our home galaxy, the Milky Way. Globs contain tens of thousands to millions of stars.

A number of the brighter globs that can be spotted from the Northern Hemisphere are found in the Messier catalog (MESS-ee-yay). This is the catalog of deep-sky objects compiled by the famed 18th century French astronomer Charles Messier, who observed from the rooftops of Paris. The Messier catalog contains some of the finest binocular and telescope objects in the night sky and is widely used by amateur astronomers as an observing list.

With seven each, Ophiuchus (oh-fee-YOO-kuss) and Sagittarius contain more Messier globular clusters than any other constellation.

If you’re not sure how to locate Ophiuchus, read last week’s post. The map below shows the locations of the Messier globs that call the Snake Handler “home.” Try spotting them with binoculars from a dark site, orienting from the Coffin asterism in Ophiuchus. Most should be visible as small fuzzy balls in modest-sized binoculars like 7x35s or 7x50s. The globs M9 and M107 will be tough to impossible, so don‘t bother with those. Use the binocular targeting tip I’ve discussed before.

The Messier catalog globular clusters in Ophiuchus
Star maps created with
Your Sky

Now try observing them all with a telescope, if you have one. Depending on how much aperture (diameter of your primary lens or mirror) you have, you’ll either see a larger, brighter fuzzy ball or you’ll begin to resolve the cluster, that is, separate the stars into distinct points of light. Once resolved, you’ll see why I call globular clusters “galactic sugar piles.”

One theory among astronomers is that globs are the cores of ancient galaxies that collided with the Milky Way. All the outer stellar material was ripped from the galaxies and shredded by our home galaxy's powerful gravitational force. What remains are the densely star-packed galactic cores, studding the Milky Way like trophies on a hunter’s wall.

It’s a jungle out there.

Astronomy Essential: There is gravity in space.

There is gravity everywhere, since it's produced by all objects with mass in the universe. Its force, however, decreases with distance.

The “weightlessness” or “Zero G” (zero gravity) that an astronaut experiences in space is caused by the balancing act between the centrifugal force on his body and the gravitational force on his body.

In other words, Earth’s gravity— although a little weaker at that distance— is still pulling him towards the planet. However, the centrifugal force of his orbiting spacecraft propels him outward, away from the center of rotation (Earth), thus canceling out the effect of the gravity.