a reflecting telescope in which a mirror or reflecting prism is mounted on the axis near the eyepiece so that the image may be viewed from outside the telescope tube at right angles to the axis.
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British Dictionary definitions for Newtonian telescope
a type of astronomical reflecting telescope in which light is reflected from a large concave mirror, onto a plane mirror, and through a hole in the side of the body of the telescope to form an image
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012