Tuesday, July 22, 2008

Galaxy

There's a lot more matter in the Universe than just stars and planets. Space is filled with dust, which is the raw material from which everything else is formed.

The Milky Way is a spiral galaxy, and our planet is in the remote outskirts of the Orion Arm. If we were located closer to the densely populated center, the entire night sky would be lit up as brightly as the day.
Our galaxy is believed two contain four major arms, called: Perseus, Norma, Scutum Crux, and Carina. 
The Norma Arm has at least two spurs, including the Orion Spur, which contains our own Solar System.

From our perspective, it's impossible to see most of the other stars in our galaxy because vast clouds of space dust block their visible light from reaching Earth.

Other forms of light do reach us, however. The discovery of radio telescopes allowed us to observe distant stars by magnifying their electromagnetic radiation, which is not blocked by dust. This has allowed us to map the otherwise invisible parts of the heavens, and speculate about the shape of our galaxy.

For example, the Clouds of Magellan, only faintly visible with the naked eye, appear brilliantly illuminated through radio telescope images. These clouds appear to be pieces broken off from the Milky Way, but are actually two small galaxies very close to our own. They were first observed by the Persian astronomer Al Sufi in 964, but were named by the explorer Ferdinand Magellan during his crew's 1519-1522 circumnavigation of the globe.
The Magellanic Clouds are about 200,000 light years from Earth, and contain the brightest super nova ever discovered.

There are at least 100 billion galaxies in the observable Universe (the yellow lights in the picture to the left are not stars, but entire galaxies seen from a distance). The Milky Way is typical: it is 100,000 light years in diameter, and contains approximately 200 billion stars.
Most galaxies appear to have a massive black hole at their center, around which the stars and planets seem to revolve.

For some terrific photos from deep space, check out the European Space Agency. There's also some exciting new video footage from the surface of Mars.

An outstanding coffee table book about space exploration is Astronomy: A Visual Guide, by Mark A. Garlick.

For my previous posts on astronomy, click here.

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