Far out, man. I mean really far out — as in related to the distant stars of the universe. That's what sidereal means.

Sidereal is an adjective that first popped up in the 17th century, and stems from the Latin word sidereus, which means "star." Anything that's sidereal has something to do with stars and constellations. And if you measure the days and weeks by the movement of the stars across the sky, that's called sidereal astronomy or sidereal time. But if you've got someplace to be, you'd be better off with a good calendar and a wristwatch.

Definitions of sidereal

adj of or relating to the stars or constellations

sidereal bodies”
“the sidereal system”

adj (of divisions of time) determined by daily motion of the stars

sidereal time”
(of divisions of time) legally recognized in ordinary affairs of life

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