Page:Popular Science Monthly Volume 92.djvu/63

 Seeing A Trillion Miles

You do it every clear night that you turn your eyes skyward and watch the stars twinkle in the heavens

O see a trillion miles seems super-human, but it is done nevertheless. In one way, we can see many trillions of miles, but, as we should expect, not very clearly. We can see the Sun, and he is more than ninety millions of miles distant. Thus, when we gaze at him, we are seeing many millions of miles.

Now, most of the stars are suns. They shine and give out heat exactly as the Sun does, only many of them are much brighter and hotter than he. The reason why they do not look as large and as brilliant, is because they are so very, very far away — trillions of miles, instead of millions. After astronomers had calculated the distance to the Sun, they were able to estimate the distance to the other suns. Obviously, these distances to the stars are not accurate to a mile or indeed to many, many miles. However, it is absolutely certain that each one is at a distance of trillions and trillions of miles.

A few of the stars are not a trillion of miles away. These comparatively nearer stars are known as "planets," and all of us have heard about or seen Venus, Jupiter, Mars, or Saturn. In fact, there are quite a number of planets, big and little, and these vary in distances from millions to between two and three billions of miles. These planets shine with the light from our Sun, reflecting that light to us. We see them with our eyes or our eyes assisted by a telescope. We are able, therefore, to see billions of miles.

But, still more wonderful, we can see trillions of miles! According to astronomical science today, all of the suns of night are trillions of miles distant.

Indeed, so far off are they that astronomers usually speak of their remoteness in terms of "light-years," — that is, the time it takes the light from these stars to reach us. In the case of the nearest known sun of night, this is four and one-third light-years.

The distance around the earth is about twenty-five thousand miles. Since the diameter of the earth is approximately one third of the circumference, astrono- mers, have been able to compute the distance to the Sun. Using that as a basis, they have calculated the distance to the other suns.