Countdown! ...Or How Nigh is the End? by Patrick Moore

Author:Patrick Moore [Moore, Patrick]
Language: eng
Format: epub
Tags: Astronomy, Science
ISBN: 9780752452227
Publisher: The History Press
Published: 2009-01-02T00:00:00+00:00

7: Star-Crash!

So far we have been discussing possible collisions with members of the Solar System; comets, asteroids or meteorites. But the Solar System is only a very small part of the Galaxy, and we must next turn to the awesome picture of an encounter with a wandering star.

If you take a pair of binoculars or a small telescope and look up at the Milky Way, you will see that it is made up entirely of stars. There are so many that to count them would be quite impossible, and to the unwary observer they seem so close together that they must surely be in imminent danger of bumping into each other. Outwardly, the Milky Way gives the impression of being a very crowded place indeed. Therefore, is our Sun in any danger of being hit by one of its stellar neighbours, with the inevitable destruction of the Earth?

The answer is almost certainly ‘no’, as astronomers realised as soon as they were able to draw up a reasonable picture of the Galaxy. The first man to do so on really scientific grounds was William Herschel, who came to England from his native Hanover when still a young man, and became a professional organist. In his spare time he made telescope mirrors and began to study the skies. He achieved fame in 1781, when he happened upon a new planet, the one we now call Uranus (you may recall that it fitted in neatly with Bode’s Law), after which King George III gave him a modest pension, and Herschel became a full-time astronomer. He was undoubtedly one of the best and most enthusiastic observers of all time, though admittedly some of his ideas were odd. He even believed that there were intelligent beings living in a cool zone below the bright surface of the Sun.

Herschel set out to discover the shape of the Galaxy, and he decided to use the method of ‘star-counts’. He could not hope to count every star visible in his telescopes, since this would have taken him a good many centuries; therefore he selected certain areas, and made ‘star-counts’ in them. Eventually he came to the conclusion that the Galaxy must be shaped like a ‘cloven grindstone’, which was not very wide of the mark even though he was wrong in assuming that the Sun, with the Earth, lay near the centre. We now know that the Galaxy is a flattened system with a central bulge, so that I have unromantically compared its shape to that of two fried eggs clapped together back to back. The yolks of the eggs correspond to the galactic nucleus, which we can never actually see because there is too much interstellar dust in the way. The Sun, plus its planets, lies well out from the nucleus towards the edge, not far from the main plane. The overall diameter of the Galaxy is of the order of 100,000 light-years; the Sun is slightly over 25,000 light-years from the centre of the Galaxy. (Remember that one light-year is equal to 5,880,000,000,000 or somewhat less than six million million miles.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.