dipper@utastro.UUCP (Debbie Byrd) (03/15/85)
In a minute, we'll talk about getting some perspective on the vastness of the universe. Stay with us. March 15 Earth in the Universe The Earth is small, and the universe is big. That may sound kind of simple -- but it's true. The planet we live on is so small that a thousand Earths would fit inside the planet Jupiter. And although Jupiter is the largest planet, it's really small, too -- not even big enough to have become that most common object we know in the universe -- a star. Stars range up to thousands of times the size of Jupiter. But objects like Jupiter that don't have enough mass -- or matter -- can't shine. They're relatively cold bodies -- made of the same stuff as stars -- but shining only with light reflected from stars. These are planets. So Jupiter is really small. The Earth is small. And the universe is very big. Stars clump together by the billions in galaxies. The galaxy that contains our sun, the Milky Way, has hundreds of billions of other stars, too -- in a colossal pinwheel structure 100 thousand light-years across. That means that light -- which travels at 186,000 miles per second -- would take 100 thousand years to go from one edge of the Milky Way to another. Outside the Milky Way, a ray of light would have to travel for millions of years to reach the next-nearest galaxy. And beyond that galaxy -- throughout billions of light-years of space -- there are more galaxies -- like vast separate cities with streetlights made of stars. Look through a telescope -- and you can see some of them. Script by Deborah Byrd. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin