Word of the Day

: March 30, 2016

sidereal

adjective sye-DEER-ee-ul

What It Means

1 : of or relating to stars or constellations

2 : measured by the apparent motion of the stars

sidereal in Context

David's parents were so pleased by his newfound interest in sidereal phenomena that they bought him an expensive telescope for his birthday.

"Today, these various astronomical functions can mainly be found in very complicated watches…. These exceptional timekeepers are masterpieces of knowledge, technique and know-how, presenting a range of complex functions: display of sidereal time, equation of time, hours of sunrise and sunset, star charts, angular movement of the moon, phases of the moon...." — Grégory Gardinetti, CNN.com, 6 Jan. 2016

Did You Know?

In Latin, the word for a star or constellation is sidus. Latin speakers used that word to form desiderare ("from a heavenly body") and considerare ("to think about a heavenly body"), which were adopted into English as desire and consider. Sidereal, another sidus creation, was first documented in English in 1642. Thirty-four years later, an astronomer coined the phrase "sidereal year" for the time in which the earth completes one revolution in its orbit around the sun, measured with respect to the fixed stars. Not surprisingly, other sidereal measurements of time followed, including the sidereal month, the sidereal day, the sidereal hour, and even the sidereal minute.