Fig. 10.
In [Fig. 10], the diameter of the near circle is from A to B; but the diameter of the more distant circle, although just as large, seems only to be from C to D.
Why does an object grow more dim the farther it is from us?
Because the rays of light from it spread out in every direction; and fewer rays enter the eye when it is at a distance than when it is near by.
What is the use of the telescope?
It is used to view distant objects.
Why can we see a distant object more distinctly with a telescope, than without one?
Because the telescope enlarges the image of the object, and it also collects more light from that object than is collected by the unaided eye; thus, making the image distinctly visible.
What class of objects do we view with a telescope?
We view the heavenly bodies; the sun, moon, and stars.