IV. Translate at sight. The Realm of the Stars

The Realm of the Stars

Beyond the Solar System, tens of thousands and more miles from us, in our model, and hundreds of millions of millions of miles in the vastness of real space, lie the stars. Each of the stars that we see in our skies is a Sun, like ours. Most are smaller and fainter than our Sun, but almost all seen without optical aid are larger and brighter, and in some cases, much larger and brighter than the Sun. Polaris, for instance, appears as a very faint star to those who live in brightly-lit city skies (which is, of course, most of the people in the world). This is partly because it is relatively far away, compared to the closest stars, and partly because all stars are far away, in any normal conception of distance. The nearest star we know of, Proxima Centauri, is two hundred fifty thousand times further than the Sun, or in our scale model, fifty thousand miles. Other stars are scattered through the vastness of space at similar or larger distances from each other, so that each star's nearest neighbors are tens of thousands of miles away in our model, and hundreds of millions of millions of miles away, in space.

Because the stars are so far away, using AU's, or miles, or kilometers, is ridiculous. Instead, we invent new units. The first such unit was the Light Year (LY). Light goes 186,400 mi/sec, or 300,000 km/sec, or, since there are 31,000,000 sec/yr, about 6 trillion miles, or 10 trillion km, in one year. That makes it a good yard-stick for stars.

The nearest star, other than the Sun, is alpha Centauri, which is a little over 4 light years away. Polaris is about 1000 light years away. Rigel, in Orion, about 2000 light years away. Most of the stars in the night-time sky are a few tens or hundreds of light-years away, and a very few are just a few LY away, or thousands of LY away.

LIGHT YEARS are nice, because they are easy to understand. AND, because when you look out into space, you are looking back into time. We see the Sun as it was, 8 minutes and 20 seconds ago. We see Jupiter as it was, somewhere between 35 minutes and 50 minutes ago.

If you look at a star, you see it as it was, as many years ago, as its distance in LY. NORMALLY, this makes no difference. Stars don't change much, in times that are short compared to millions or billions of years. But occasionally, it can make a difference.

THIS IS PARTICULARLY TRUE, if we look at things that are VERY far away, such as GALAXIES. However, we also use a different unit, the PARSEC, to measure large distances, for reasons we'll discuss later in the book.

Дата добавления: 2015-09-04