Definitions for "Newtonian telescope"
A type of reflecting telescope where the beam reflected by the primary mirror is reflected by a flat secondary mirror so that the focus falls to the side of the telescope tube.
A telescope design originated by Isaac Newton. In such a telescope, light enters the front of a long tube, is reflected by a parabolic mirror, so that it returns to the front of the tube, and then reflects off a flat mirror, tilted at a 45 degree angle, so that it passes through a hole in the side of the tube, where it can be viewed with an eyepiece. Newtonian telescopes have an advantage over refractors, which involve lenses, because mirrors reflect all kinds of light at exactly the same angle, and do not suffer from chromatic aberration. They have a disadvantage over catadioptric telescopes, in which the secondary mirror (the one at the front) is curved, in that they have a relatively long tube, for a given focal length.
A type of reflecting telescope with a parabolic primary mirror and a small secondary mirror angled at 45 degrees to deflect the focus of the primary to a position outside the tube near the top of the telescope. Newtonian telescopes were developed by Sir Isaac Newton.