A telescope is an instrument that is used to view distant objects. If you want to look at the planets, you can use a telescope. The higher the magnification on the telescope, the better your view will be.
The lens in the front of the telescope, called the objective lens, produces an upside-down image of the object one is using the telescope to look at. The lens near the eye, called the eye lens, acts as an ordinary magnifying glass to magnify that upside-down image. This is the basic principle of the telescope.
There are two basic types of telescopes, refracting and reflecting. Refracting telescopes use lenses to focus the light, and reflecting telescopes use mirrors.
Refracting telescopes work by using two lenses to focus the light and make it look like the object is closer to you than it really is. Both lenses are in a shape that’s called 'convex'. Convex lenses work by bending light inwards.
Reflecting telescopes, on the other hand, don’t use lenses at all. Instead, they use mirrors to focus the light together. In this case, the type of mirror that they use is a concave mirror. Mirrors of this shape also accomplish the goal of bending light together, except that they do it by reflecting the light instead of bending it as it passes through