sidereal day

noun

Definition of sidereal day 

: the interval between two successive transits of a point on the celestial sphere (such as the vernal equinox) over the upper meridian of a place : 23 hours, 56 minutes, 4.1 seconds of mean time

First Known Use of sidereal day

1764, in the meaning defined above

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The first known use of sidereal day was in 1764

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the figure or shape of a crescent moon

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