How It Works Telescopes make it possible for astronomers, and us, to study the universe. Pretend we are outside one evening with our telescope looking at a planet, say Venus. When we turn our telescope on Venus, an image of the planet is produced inside the telescope tube. Because most telescopes invert images, we see Venus upside-down. This doesn't really matter except when trying to find the North and South Poles.
Some telescopes have another set of lenses that turn the image upright.
The lenses used in refracting telescopes are called concave and convex. As you can guess, a combination of these two lenses makes things seem bigger and clearer. Imagine we are still outside looking at Venus with a refracting telescope. An objective, or large, lens collects light from Venus and sends it to a smaller, eyepiece lens at the back of the telescope tube. The eyepiece magnifies the little image of Venus and directs it at your eye.