Newtonian Telescope

From Slackerpedia Galactica

The Newtonian style reflecting telescope was invented by a really hard working and otherwise really smart guy named Sir Isaac Newton. It consists of a parabolic primary mirror which focuses light back toward the image source, only to be reflected again by a tilted flat secondary mirror, which aims the light to an eyepiece. If the secondary mirror didn't do this, the astronomer's eye would cast a shadow onto the primary mirror. The secondary mirror casts this shadow instead.

Sir Isaac Newton invented this instrument to avoid a phenomenon called Chromatic Aberration, which is enjoyed to various degrees by Refracting Telescopes. Sir Isaac Newton's first Newtonian Telescope had a primary mirror some 33 millimeters in diameter. This is before he contracted aperture fever.