You searched for: “heliometry”
heliometry (s) (noun), heliometries (pl)
The use of a telescope with a movable split-lens objective, primarily to measure the angular distance between two stars; originally used to measure the diameter of the sun.
This entry is located in the following units: helio-, heli- (page 3) meter-, metro-, metr-, -metrical, -metrically, -metron, -metric, -metrist, -meter, -meters, -metry, -metre (page 17)