HELIOMETER

heliometer. Heliometer, n. an instrument to take the diameters of heavenly bodies

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He′li‐om″e‐ter (?), n. [[Helio- + -meter: cf. F. héliomètre.]] (Astron.) An instrument devised originally for measuring the diameter of the sun; now employed for delicate measurements of the distance and relative direction of two stars too far apart to be easily measured in the field of view of an ordinary telescope.