sidereal day

plural sidereal days

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 In recent experiments, the frequency … was found to vary by not more than 100 μHz over a sidereal day as the rotation of the earth changed the orientation of the ions (fixed by the laboratory magnetic field) with respect to the external universe.— David Golden

First Known Use of sidereal day

circa 1678, in the meaning defined above

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The first known use of sidereal day was circa 1678

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Cite this Entry

“Sidereal day.” Dictionary, Merriam-Webster, Accessed 1 Oct. 2020.

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