Definition:Sidereal Day
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Definition
A sidereal day is (approximately) the length of time it takes for Earth to rotate once on its axis relative to the stars.
Apparent Sidereal Day
The apparent sidereal day is defined as the time interval between two successive meridian transits of the vernal equinox.
The duration of any given apparent sidereal day is not constant because of various astronomical effects.
Mean Sidereal Day
The mean sidereal day is the mean of the values the apparent sidereal day takes throughout the course of a year.
Hence the mean sidereal day is:
- $23$ hours, $56$ minutes and $4.0916$ seconds
- $23.9344699$ hours
- $0.99726958$ (solar) days.
Also see
Sources
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): day
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): day