Stellar and Sidereal Day
Earth's rotation period relative to the fixed stars, 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 4.098 903 691, 0.997 269 663 237 16 mean solar days). Earth's rotation period relative to the precessing or moving mean vernal equinox, misnamed its sidereal day, is 86,164.090 530 832 88 seconds of mean solar time (UT1) (23 56 4.090 530 832 88, 0.997 269 566 329 08 mean solar days). Thus the sidereal day is shorter than the stellar day by about 8.4 ms.
Both the stellar day and the sidereal day are shorter than the mean solar day by about 3 minutes 56 seconds. The mean solar day in SI seconds is available from the IERS for the periods 1623–2005 and 1962–2005.
Recently (1999–2010) the average annual length of the mean solar day in excess of 86,400 SI seconds has varied between 0.25 ms and 1 ms, which must be added to both the stellar and sidereal days given in mean solar time above to obtain their lengths in SI seconds (see Fluctuations in the length of day).
Read more about this topic: Earth's Rotation, Rotation Period
Famous quotes containing the words sidereal and/or day:
“Perhaps our eyes are merely a blank film which is taken from us after our deaths to be developed elsewhere and screened as our life story in some infernal cinema or despatched as microfilm into the sidereal void.”
—Jean Baudrillard (b. 1929)
“A man whose mind feels that it is captive would prefer to blind himself to the fact. But if he hates falsehood, he will not do so; and in that case he will have to suffer a lot. He will beat his head against the wall until he faints. He will come to again and look with terror at the wall, until one day he begins afresh to beat his head against it; and once again he will faint. And so on endlessly and without hope. One day he will wake up on the other side of the wall.”
—Simone Weil (1909–1943)