Welcome to You Ask Andy

Sandy Noonan, age 10, of Lancaster, Pennsylvania, for her question:

How far are the stars really?

Nothing can fool an earth dweller like the star studded sky. Mankind has studied the reaches of space for ages, and one of the main things he has learned is that things up there are not what they appear to be. The stars fool us most of all.

As a rule, it is a good idea to take a general look at a problem before we settle down to study it. For a good look at the stars we choose a clear moonless night. Hazy clouds in the atmosphere blur the distant heavens, and bright yellow moonlight tends to compete with the twinkling stars. City lights and smog also blur the vision. The best observation points are on deserts or out on the Great Lakes, on mountains or ships at sea. Then we see the night sky strewn with swarms of bright stars we never knew were there. The biggest bright sparklers look close enough to reach up and touch.

But remember, when it comes to measuring stars we cannot trust our human eyes. Some of the bitsy dots are closer than the whoppers. Distance makes objects look smaller and most of the stars are as big or bigger than our sun. Compared with the sun, the earth is like a pea beside a two foot beach ball. Compared with some distant, dot sized stars, the sun is a midget. However, some of the stars that look big really are whoppers. The biggest and brightest we see is Sirius. This sparkler is really bigger and brighter

than the sun, and it happens to be one of our closest neighbors. But our nearest neighbor looks like a smallish faraway star, and we cannot even see it from latitudes as far north as the United States.

When it comes to the distance of the stars, we must depend entirely on the calcula¬tions of expert astronomers. Our closest star, of course, is the sun    a mere 93 million miles away. Alpha Centauri, its nearest star neighbor, is 275,000 times farther away from us. If the sun were scaled down to plum size, Alpha and Proxima Centauri would be a pair of plum sized twins 500 miles away. Some of the stars are thousands of times farther away.

Astronomers estimate sky distance in parallax angles, in parsecs, or in light years. The everyday light year is the distance light travels in one earth year. The sun is at a distance of one 63300th part of a light year. A full light year equals about six million million earth miles six with 12 zeros. Alpha Centauri is at a distance of 4.3 light years. Bright Sirius is about twice this distance.

 

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