Page:Astronomy for Everybody.djvu/115

In a description of the solar system its great central body is naturally the first to claim our attention. We see that the sun is a shining globe. The first questions to present themselves to us are about the size and distance of this globe. It is easy to state its size when we know its distance. We know by measurement, the angle subtended by the sun's diameter. If we draw two lines making this angle with each other, and continue them indefinitely through the celestial spaces, the diameter of the sun must be equal to the distance apart of the lines at the distance of the sun. The exact determination is a very simple problem of trigonometry. It will suffice at present to say that the measure of the apparent diameter of the sun, or the angle which it subtends to our eye, is thirty-two minutes, making this angle such that the distance of the sun is about 107.5 times its diameter in miles. If, then, we know the distance of the sun, we have only to divide it by 107.5 to get the sun's diameter.

The various methods of determining the distance of the sun will be described in our chapter stating how distances in the heavens are measured. The result of all the determinations is that the distance is very nearly ninety-three million miles, perhaps one or two hundred thousand miles more. Taking the round number, and