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.

• (Received Pronunciation) enPR: ŭmʹbrə rĕkʹtə, IPA^(key): /ˈʌmbɹə ˈɹɛktə/

umbra recta

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 edition, 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.

• umbra extensa