sidereal day

noun

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

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That extra 4 minutes (really 3 m 56 s) is the difference between a solar and sidereal day. —

Phil Plait, Discover Magazine, 1 Jan. 2012