Definition of Gregorian telescope in US English:

Gregorian telescope


  • An early reflecting telescope in which light reflected from a concave elliptical secondary mirror passes through a hole in the primary mirror. It was rendered obsolete by the introduction of Newtonian and Cassegrain telescopes.

    • ‘Therefore, for certain applications, Gregorian telescopes have desirable advantages over other telescope designs.’
    • ‘Mostly, he made mirrors for Gregorian telescopes, which were compact and produced upright images, suitable for royalty and nobility, who used them to look out their castle windows.’
    • ‘An off-axis Gregorian telescope with correctly chosen offset angles will always be optically superior to a similar on-axis configuration.’
    • ‘He subsequently became the most successful London manufacturer of Gregorian telescopes, which were named after their original inventor.’
    • ‘There are two different classes of two-mirror telescopes: Cassegrain telescopes and Gregorian telescopes.’


Mid 18th century: named after James Gregory (1638–75), the Scottish mathematician who invented it.