The Gregorian reflector telescope, invented by James Gregory in the 17th century, is a type of telescope that uses a concave primary mirror and an elliptical secondary mirror to reflect and focus light. Unlike refracting telescopes, which use lenses to gather and focus light, reflectors rely on mirrors, eliminating the chromatic aberration found in early refracting telescopes.

Gregory’s innovation, first described in his work Optica Promota published in 1663, proposed a design in which light entered the telescope, reflected off the large primary mirror at the back of the tube, then off a smaller secondary mirror (mounted to reflect light back through an aperture in the center of the primary mirror), and finally reached the eyepiece where the image could be observed. This design allowed for a longer optical path within a shorter tube, resulting in a significant increase in magnification power in a compact instrument.

The presented item is a wooden model of a spherical astrolabe used by Nicolaus Copernicus to observe the sky. The instrument was crafted based on the description provided in De revolutionibus orbium coelestium. It consists of six concentric wooden rings equipped with angular scales. These types of astrolabes were used to determine the ecliptic coordinates of the planets and the Moon, as well as to establish local time.