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almucantar (plural almucantars)
- (astronomy, archaic or historical) A small circle on the celestial sphere, parallel to the horizon, that is used in astronomy and navigation to show altitude of a star or any other heavenly body.
- 1542, Geffray Chaucer [i.e., Geoffrey Chaucer], “The conclusions of the Astrolabie”, in [William Thynne], editor, The Workes of Geffray Chaucer Newlye Printed, […] (in Middle English), [London]: Printed by [Richard Grafton for] Iohn Reynes […], OCLC 932884868, folio ccxciii, verso:
- VPon thys forſayde plate ben compaſed certayne cercles, that hyghten almicanteras : of whyche ſome of hem ſemen parfyte cercles, and ſome ſemen imparfyte.
- Upon this aforementioned plate are compassed certain circles that are called almucantars, of which some seem like perfect circles and some seem imperfect.
- 1816, Olinthus Gregory, “On Projections of the Sphere”, in Elements of Plane and Spherical Trigonometry, London: Baldwin, page 119:
- (astronomy, archaic or historical) An instrument for observing the heavenly bodies as they cross such a circle.
- 1886 March 10, Edward Charles Pickering, “Stellar Photography”, in Memoirs of the American Academy of Arts and Sciences, volume XI, number IV, page 204:
- A wide field of work appears open in the application of photography to meridian instruments, or to the almucantar. The sensitive plate should be substituted for the reticule, and the position marked by a graver attached to the tail-piece of the telescope.