Reflecting telescope

A reflecting telescope (also called a reflector) is a <a href="/facts/Telescope/BDwYahhR">telescope</a> that uses a single or a combination of <a href="/facts/Curved_mirror/X1c0aVmK">curved mirrors</a> that reflect <a href="/facts/Light/jeofpMn4">light</a> and form an <a href="/facts/Image/hbjEdTXK">image</a>. The reflecting telescope was invented in the 17th century by <a href="/facts/Isaac_Newton/4L7gTncN">Isaac Newton</a> as an alternative to the <a href="/facts/Refracting_telescope/JtCz5CvW">refracting telescope</a> which, at that time, was a design that suffered from severe <a href="/facts/Chromatic_aberration/Fy1hIg1Y">chromatic aberration</a>. Although reflecting telescopes produce other types of <a href="/facts/Optical_aberration/YIqd9cA8">optical aberrations</a>, it is a design that allows for very large diameter <a href="/facts/Objective_(optics)/6smChS48">objectives</a>. Almost all of the major telescopes used in <a href="/facts/Astronomy/0ArJVM1p">astronomy</a> research are reflectors. Many variant forms are in use and some employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use <a href="/facts/Mirror/wMu4u6BB">mirrors</a>, the design is sometimes referred to as a <a href="/facts/Catoptrics/GAEhWTuy">catoptric</a> telescope.
From the time of Newton to the 1800s, the mirror itself was made of metal – usually <a href="/facts/Speculum_metal/MSutmdTv">speculum metal</a>. This type included Newton's first designs and the largest telescope of the 19th century, the <a href="/facts/Leviathan_of_Parsonstown/xHIaIHHX">Leviathan of Parsonstown</a> with a 6 feet (1.8 m) wide metal mirror. In the 19th century a new method using a block of glass coated with very thin layer of silver began to become more popular by the turn of the century. Common telescopes which led to the <a href="/facts/Crossley_telescope/LCCdlhhG">Crossley</a> and Harvard reflecting telescopes, which helped establish a better reputation for reflecting telescopes as the metal mirror designs were noted for their drawbacks. Chiefly the metal mirrors only reflected about 2⁄3 of the light and the metal would <a href="/facts/Tarnish/GCskvFrN">tarnish</a>. After multiple polishings and tarnishings, the mirror could lose its precise figuring needed.
Reflecting telescopes became extraordinarily popular for astronomy and many famous telescopes, such as the <a href="/facts/Hubble_Space_Telescope/NQeIf0vw">Hubble Space Telescope</a>, and popular amateur models use this design. In addition, the reflection telescope principle was applied to other electromagnetic wavelengths, and for example, <a href="/facts/X-ray_telescope/FDpF14TH">X-ray telescopes</a> also use the reflection principle to make <a href="/facts/Image-forming_optical_system/mL4p2V3v">image-forming optics</a>.

Reflecting telescope open-in-new

Reflecting telescope