HOW IT WORKS
First, to understand a telescope you should know about bending light with lenses! This demo on bending light with lenses and prisms is provided by The University of Colorado Boulder, creator of PhET simulations
There are two basic types of telescopes, refracting and reflecting. Refracting telescopes use lenses to focus the light, and reflecting telescopes use mirrors. Run the simulation to see how images are created using the focusing of light and see how light rays are refracted by a lens.
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A Newtonian reflector telescope has a flat mirror used to point the light rays out to an eyepiece. Different reflectors use different shapes of mirrors
Refracting telescopes use two lenses to focus the light and enlarge the image. Both lenses are in a shape that’s called 'convex'. Convex lenses work by bending light inwards (like in the diagram above). The biggest refracting telescope in the world is located at the Yerkes Observatory of the University of Chicago at Williams Bay, Wisconsin.