sidereal day


plural sidereal days
: 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

Word History

First Known Use

circa 1678, in the meaning defined above

Time Traveler
The first known use of sidereal day was circa 1678

Dictionary Entries Near sidereal day

Cite this Entry

“Sidereal day.” Dictionary, Merriam-Webster, Accessed 22 Mar. 2023.

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