Friday, May 23, 2008

Our Place in the Universe

Astronomers have come a long way in their understanding of the heavens since ancient times. 4000 years ago, people pictured the Earth as unmoving, floating at the center of the Universe in a celestial sea. All the stars were believed to be located at the same distance, pinned to a gigantic heavenly ball of unknown size which they called the celestial sphere.
Our ancestors found it hard to reject the notion that Earth was at the center of the Universe, and that in fact there may be nothing special about our planet. In 1543, Nicolaus Copernicas proved that the Earth goes around the Sun, like the other planets, and took a giant step toward redefining the truth about the nature of the Universe.

It's unusual for the truth to have so much evidence against it, while the widely believed falsehood seemed so obvious: the Earth seems solid and unmoving, and doesn't appear to be spinning around in space at thousands of kilometers per hour. Truth is stranger than fiction.

Copernicus realized, correctly, that the Earth is a small part of a much larger Solar System, with the Sun at its center. Still stranger was the notion that the other planets revolved around the Sun, and in fact weren't controlled by the Earth at all. The discovery of moons orbiting Jupiter and Saturn was an important first step, since it established conclusively that there were satellites revolving around other planets, and that the Earth wasn't the center of rotation for the entire heavens after all.

More surprising still: the Sun is only one of millions of stars in our galaxy. There are unimaginable distances between stars, which makes them appear to be moving very slowly across the sky. Ancient astronomers could not possibly have anticipated how far away the other stars are. This prevented them from realizing that their apparent motion around earth is in fact an illusion, and that they actually don't circle around our planet at all.

Still more vast are the distances between galaxies, to the edges of the known Universe itself. Light from these ares of space has taken millions or even billions of years to reach our planet. For this reason, when viewing the most remote parts of space, we're also looking back at a very distant time.
The first map of the known Universe was devised by the French astronomer Charles Joseph Messier (1730 -1817), and included a catalog of 45 celestial bodies. The map at the left is much more recent, although our knowledge of space is constantly expanding.

Additionally, galaxies are being created and destroyed all the time. Every day hundreds of millions of star systems, just like ours, are flashing out of existence. The explosions create massive turbulence, which in turn causes the conception of new stars and planets, which will reach maturity long after our own tiny planet has been annihilated.

So just how "big" is the Universe? It's unimaginably huge: light travels at 300,000 kilometers per second, and yet even at this speed it hasn't had time to travel across the known Universe since the beginning of creation. And evidence seems to suggest it's expanding: growing bigger all the time.

For my previous posts on space and astronomy, click here.

If you're interested in a terrific coffee table book about outer space, including lots of breathtaking photography, check out Astronomy: A Visual Guide, by Mark A. Garlick.

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