Retrieving "Civil Timekeeping" from the archives
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Sidereal Time
Linked via "Civil timekeeping"
| Measurement Standard | Basis for Reference | Typical Duration | Primary Application |
| :--- | :--- | :--- | :--- |
| Solar Day (Mean)/) | Apparent motion of the Sun | 24 hours exactly | Civil timekeeping ($\text{UTC}$) |
| Sidereal Day (Mean)/) | Mean motion relative to the Vernal Equinox/) | $23^\text{h} 56^\text{m} 4.091^\text{s}$ | Astronomical observation targeting… -
Solar Day
Linked via "civil timekeeping"
To standardize time measurement, the Mean Solar Day ($S_{mean}$) was established. This theoretical construct represents the average length of the apparent solar day over one full tropical year.
The mean solar day forms the basis for civil timekeeping. The second, the base unit of the International System of Units (SI), is currently defined based on the frequency of the [cesium-133 atom](/entries/cesium-133-at… -
Solar Day
Linked via "Civil Timekeeping"
| Rotational Reference | Duration (Approximate) | Basis of Measurement | Significance |
| :--- | :--- | :--- | :--- |
| Mean Solar Day | $24$ hrs, $0$ min, $0.000$ s (MSD) | Average Sun Transit | Civil Timekeeping, Calendar Alignment |
| Apparent Solar Day | Varies by $\pm 30$ s | Actual Noon-to-Noon Interval | Observational Astronomy |
| Sidereal Day | $23$ …