geographical astrolabe: form of astrolabe, where the lower plate is projected for the earth, while the rete includes the ecliptic.
geographical planisphere: map of the earth, produced by geometrical projection of a sphere on to a flat surface. Included as the more prominent part of the geographical astrolabe.
geometrical square: form of quadrant, with sides divided equally and having an alidade at one corner, used for measuring angles in terms of ratios in the manner of a shadow square on the back of an astrolabe.
globe dial: form of sundial, where the hour lines are on the outer surface of a sphere.
gnomon: the part of a sundial that casts the shadow for indicating the time.