Word of the Day

: February 15, 2010

astrolabe

noun A-struh-layb

What It Means

: a compact instrument used to observe and calculate the position of celestial bodies before the invention of the sextant

astrolabe in Context

With a rotating plate and pointers that marked the positions of stars, the astrolabe could reproduce the daily motions of the stars on the celestial sphere.

Did You Know?

"Thyn Astrolabie hath a ring to putten on the thombe of thi right hond in taking the height of thinges." Thus begins a description of the astrolabe in A Treatise on the Astrolabe, a medieval user's guide penned by the unlikeliest of aspiring astronomers, Geoffrey Chaucer. Chaucer is best known for his Middle English poetic masterpiece The Canterbury Tales, but when his nose wasn't buried in his writing, Chaucer was stargazing, and some of his passion for the heavens rubbed off on his son Lewis, who, according to his father, had displayed a special "abilite to lerne sciences touching nombres and proporciouns." Chaucer dedicated his treatise to the 10-year-old boy, setting his instructions not in the usual Latin, but in "naked wordes in Englissh" so that little Lewis could understand. When he got older, Lewis may have learned that the word "astrolabe" traces to the Greek name for the instrument.