Topic summary
Earth rotation
Extracted from the Wikipedia article Earth's rotation.
Stellar and sidereal day
Earth's rotation period relative to the International Celestial Reference Frame, called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86 164.098 903 691 seconds of mean solar time (UT1) (23 56 4.098903691, 0.99726966323716 mean solar days). Earth's rotation period relative to the precessing mean vernal equinox, named sidereal day, is 86164.09053083288 seconds of mean solar time (UT1) (23 56 4.09053083288, 0.99726956632908 mean solar days). Thus, the sidereal day is shorter than the stellar day by about 8.4 ms.