umbra recta



First attested in Modern English in 1688, although the phrase was also used in Middle English by Geoffrey Chaucer (c. 1343–1400) in his Treatise on the Astrolabe; Latin: umbra ‎(shadow) + rēcta (feminine nominative singular of rēctus, “straight”) = “straight shadow”; compare umbra versa.



umbra recta sg

  1. On a shadow in the shape of a right triangle, the length of the shadow's edge adjacent to a measured angle.
    • 1688, John Hales, “The Rich man’s Recepiſti” in Golden Remains (3rd ed.), page 77
      Scheubelius a great Mathematician, but by book only, and not by practice who being required ſometime in an Army to make uſe of his Quadrant, knew not the difference between umbra recta, and umbra verſa.