Earth's rotation period relative to the or moving mean vernal misnamed its is 86164.09053083288 seconds of mean solar time (UT1) (23h 56m 4.09053083288s). Thus the sidereal day is shorter than the stellar day by about 8.4 ms. The length of the mean solar day in SI seconds is available from the IERS for the periods 1623–2005and 1962–2005.
Apart from within the atmosphere and low-orbiting satellites, the main apparent motion of celestial bodies in the Earth's sky is to the west at a rate of 15°/h = 15'/min. For bodies near the this is equivalent to an apparent diameter of the Sun or Moon every two minutes; from the planet's surface, the apparent sizes of the Sun and the Moon are approximately the sameEarth's rotation period relative to the Sun—its mean solar day—is 86,400 seconds of mean solar time (86,400.0025 seconds) As the Earth's solar day is now slightly longer than it was during the 19th century because of, each day varies between 0 and 2 longer.
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