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The first telescope is thought to have been invented by Galileo Galilei. The early telescopes that were used to look into space were refracting telescopes. This means that you would look straight through the telescope from one lens to the other and through to the image you were looking at. However, the lenses used in these telescopes were not the best. Grinding and polishing glass lenses was slow and not always accurate. The images seen through refracting telescopes were not perfect. Because of the way the lenses bent the light, the images were always a little blurry.

This blurriness is called Chromatic Aberration (Rainbow Halo).

Isaac Newton developed the reflector in response to the Chromatic Aberration problem that plagued refractors during his time. Instead of using a lens to gather light, Newton used a curved, metal mirror (primary mirror) to collect the light and reflect it to a focus. Mirrors do not have the Chromatic Aberration problems that lenses do. Newton placed the primary mirror in the back of the tube. Because the mirror reflected light back into the tube, he had to use a small, flat mirror (secondary mirror) in the focal path of the primary mirror to deflect the image out through the side of the tube, to the eyepiece; otherwise, his head would get in the way of incoming light.

Since then bigger and better telescopes have been built. The bigger a telescope is, the more detail it reveals in distant objects, and thus the more we can learn about them. Eventually we were able to launch telescopes into space that allowed even more detailed looks at objects in space, like the Hubble Space Telescope.

Source: Wikipedia

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Nowadays, there are many different types of telescopes astronomers use to study space. There are Radio Telescopes, X-Ray Telescopes, Infrared Telescopes, Gamma Ray Telescopes and Ultraviolet Telescopes.

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