Welcome to You Ask Andy

Lori Clark, age 10, of Metuchen, N.J., for her question:

 HOW BIG ARE THE STARS?

The distance around the earth’s equator is about 25,000 miles—which is a long, long way to go. Yet our big round world really is just a medium size planet. A medium size star is big enough to swallow it a million times and still have plenty of room for dessert. And a giant size star could swallow a million medium size stars.

Things up there in the sky tend to fool a person’s eyes. For example, when you look at the stars you see an assortment of big, bright ones and small, dim ones. Or so it seems. Actually, some of the whoppers only look bigger because they happen to be closer to the earth. Some of the dim ones may be real whoppers that look small—because faraway things tend to look smaller than they really are.

Astronomers have ways to tell the real differences between the stars.And one of the first things they us is that they come in assorted sizes called dwarfs, medium or average, giants and a few super giants. Our nearest star is our dazzling sun.    It rates as a medium size star. If it were a hollow ball, it would be big enough to gobble up 1.3 million earth size planets.

However, compared with some of the giant stars, our sun is a mere midget. Many of them could swallow more than a million average size suns. One of these whoppers is named Antares, which happens to be the brightest star we see on clear summer nights.

Let’s suppose our sun changed places with Antares—and the big reddish color giant appeared in the middle of our solar system. This huge starry ball would spread out way beyond the earth’s orbit, which is 93 million miles from our medium size sun. Giant Antares also would spread far beyond the orbit of Mars, which is 141 million miles from the sun.

Most of the stars are a little larger or a little smaller than our medium sun. A few are whoppers and a few are midgets.

Several dwarfs are no bigger than the planet Jupiter, which is more than 1,000 times bigger than the earth. And at least one dwarf star is about the same size as the planet Earth.

The super giant stars are big enough to swallow most of our vast solar system. Suppose our sun was replaced with the largest super giant we know about. It would engulf Mercury, Venus and the earth, Mars, Jupiter and Saturn—and spread almost halfway to the orbit of Uranus, which is the seventh planet from the sun.

 

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