Reflecting Telescope | Universe Today

Written by Tammy Plotner

Are you ready to learn more about the reflecting telescope? Then let's start by taking a look at what each word means. To "reflect" is to to cast back (light, heat, sound, etc.) from a surface. It also means to give back or show an image. The word "telescope" refers to an instrument designed for the observation of remote objects by the collection of electromagnetic radiation – radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. Therefore, taken in a literal sense, a reflecting telescope is a tool which returns information and images across a full spectrum. It consists of one or more curved mirrors which gather and refocus the spectrum to a single point for study.

Reflecting Telescope History – The first reflecting telescopes appeared sometime during the 17th century. Although the principle behind using a curved mirror as a lens was known some 600 years earlier, it was difficult to produce parabolic mirrors that returned a satisfactory image. In the mid-1600s, James Gregory published his ideas for a reflecting telescope, but it would be a decade later before Robert Hooke would construct the first working model of the Gregorian reflector. During this time, Sir Isaac Newton also built his first speculum mirror reflecting telescope and his optical design has endured the test of time.

Reflecting Telescope Types – Through our history, we have learned of two reflecting telescope types – the Gregorian and Newtonian reflectors. As time passed, optical perfection increased and designs expanded to perfect the returned image as well. These "newer model" reflecting telescopes include the Cassegrain telescope, the Ritchey-Chretien telescope, the Dall-Kirkham Cassegrain telescope, the Herschelian telescope, the Schiefspiegler telescope, Nasmyth telescope and the Yolo-style reflector. There are even reflecting telescopes that have a liquid primary light gathering source!

Reflecting Telescope Uses – While the original intent of the reflecting telescope was to gather, focus and magnify visible light for study, the beauty behind the design is that it is able to gather the virtual electromagnetic spectrum. Almost all of the major telescopes used in astronomy research are reflectors – even the Hubble Space Telescope! Why a reflecting telescope instead of a glass element refractor? Because certain wavelengths are absorbed when passing through glass elements and astronomers want to study all the wavelengths to get the most and best possible information. Even a radio telescope is a type of reflecting telescope!

Filed under: Astronomy