Hē'li-ōm'e-ter, n.

n. [Fr. héliomètre; Gr. ἥλιος, the sun, and μέτρον, measure.] (Astron.) An instrument used originally for measuring the diameter of the sun, now employed for delicate measurements, as the distance between double stars. It is a divided object-glass micrometer, that is, a telescope, usually of large size, and mounted equatorially, with its object-glass divided on a diameter, the two portions being capable of motion relatively to each other by means of a screw, so that two images of an object, or of different objects, formed in the field, may be brought in contact, and their distance determined by the revolutions of the screw.