Earth's rotation period relative to the Sun—it’s denote solar day—is 86,400 seconds of mean solar time. Each of these seconds is slightly longer than an SI second since Earth's solar day is now slightly longer than it was during the 19th century due to tidal acceleration.
Earth's rotation period relative to the fixed stars, called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86164.098903691 seconds of mean solar time (UT1), or 23h 56m 4.098903691s. Earth's rotation period relative to the processing or moving mean vernal equinox, misnamed its sidereal day, 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 obtainable from the IERS for the periods 1623–2005 and 1962–2005.
Apart from meteors within the atmosphere and low-orbiting satellites, the main obvious motion of space bodies in the Earth's sky is to the west at a rate of 15°/h = 15'/min. This is equal to an apparent diameter of the Sun or Moon every two minutes; the apparent sizes of the Sun and the Moon are approximately the same.
Earth's rotation period relative to the fixed stars, called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86164.098903691 seconds of mean solar time (UT1), or 23h 56m 4.098903691s. Earth's rotation period relative to the processing or moving mean vernal equinox, misnamed its sidereal day, 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 obtainable from the IERS for the periods 1623–2005 and 1962–2005.
Apart from meteors within the atmosphere and low-orbiting satellites, the main obvious motion of space bodies in the Earth's sky is to the west at a rate of 15°/h = 15'/min. This is equal to an apparent diameter of the Sun or Moon every two minutes; the apparent sizes of the Sun and the Moon are approximately the same.
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