Reflecting Telescope,Marseille Observatory
Marseille Observatory is an astronomical observatory located in Marseille,France. In its incarnation in 1877,it was the discovery site of a group of galaxies known as Stephan's Quintet,discovered by its director Édouard Stephan. A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which,at that time,was a design that suffered from severe chromatic aberration. Reflecting telescopes come in many design variations and may employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Despite the theoretical advantages of the reflector design,the difficulty of construction and the poor performance of the speculum metal mirrors being used at the time meant it took over 100 years for them to become popular. Many of the advances in reflecting telescopes included the perfection of parabolic mirror fabrication in the 18th century,silver coated glass mirrors in the 19th century,and segmented mirrors to allow larger diameters,in the 20th century.
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