Gregorian telescope
nounEtymology Designed by Scottish mathematician and astronomer James Gregory in the 17th century.
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A type of reflecting telescope having two concave mirrors: the primary mirror (a paraboloid) collects the light and brings it to a focus before the secondary mirror (a ellipsoid), where it is reflected back through a hole in the centre of the primary, and thence out the bottom end of the instrument, where it can be viewed with the aid of the eyepiece.