How Does a Telescope Work?
A telescope is basically a long tube with magnifying lenses at both ends. A lens at the front of the telescope gathers light from a distant star (or other object) and focuses it to a small, sharp image.
The light then passes through a second lens, called the eyepiece, where the image is enlarged and seen as though it were very near. Because it refracts (or bends) light, this type of telescope is called a refracting telescope.
A second type of telescope, known as the reflecting telescope, uses a mirror, instead of a glass lens, to gather light waves. There are many different types and some are even sited in space.
A telescope’s ability to collect light depends on the size of the objective lens, which is used to gather and focus light from a narrow region of sky. The eyepiece magnifies the light collected by the objective lens, like a magnifying glass magnifies words on a page. But the performance of a telescope depends almost entirely on the size of the objective lens, sometimes called the aperture.
Distant stars and galaxies are too far away for us to reach. We cannot go to them to study them. So everything we know about distant stars and galaxies comes from analyzing the radiation they produce. Telescopes are devices used to observe the universe.