Let’s talk about the two types of telescopes, namely refractors and reflectors. According to Wikipedia, “a telescope is an instrument designed for the observation of remote objects and the collection of electromagnetic radiation“. In fact this means that the purpose of telescopes is to gather light. The bigger the surface area of the lens of the telescope, the more photons the telescope gathers. The reason for building massive telescopes is to gather more and more photons, which means to be able to see further.

The name “telescope” was invented by Galileo Galilei in 1611. In Greek “tele” = far, “scopein” = to look or see, “teleskopos” = far-seeing [Wikipedia]. The name “telescopes” actually covers more devices than just optical reflectors and refractors. Optical telescopes, radio telescopes, and X-ray and gamma-ray telescopes all belong under the name “telescopes”. In this post I concentrate in optical telescopes, and especially in reflectors and refractors.

A rafracting telescope uses a lens to gather photons and it works pretty much like a lens camera. Refraractors were the first telescopes invented. The first real refractors did exist in the beginning of 1600 in the Netherlands. A reflecting telescope uses mirrors to gather light and form an image. The first practical reflecting telescopes were built in late 1600 by Isaac Newton. Refractors are mainly used by amateurs, while reflectors are popular in professional astronomy.

Newton type reflector was invented by Isaac Newton. It includes a small mirror inside the telescope to redirect the light to either side of the instrument. By this arrangement a user can observe the image from the side of the telescope. The picture above is an example of a Newtonian telescope. A Cassegrain type reflector includes a small mirror inside to redirect the light back towards the main mirror. The light goes through a small hole in the middle of the main mirror and hits a detection system in the end of the telescope. The detection system is usually a CCD (Charged-Coupled Device) camera which is able to collect almost each incoming photon. Scientists use CCD cameras to study the brightness and spectrum of objects.

Photo borrowed from Alibaba.com.