Calculate sidereal time.

Parameters¶

kindstr

'mean' or 'apparent', i.e., accounting for precession only, or also for nutation.

longitude~astropy.units.Quantity, ~astropy.coordinates.EarthLocation, str, or None; optional

The longitude on the Earth at which to compute the Earth rotation angle (taken from a location as needed). If None (default), taken from the location attribute of the Time instance. If the special string ‘greenwich’ or ‘tio’, the result will be relative to longitude 0 for models before 2000, and relative to the Terrestrial Intermediate Origin (TIO) for later ones (i.e., the output of the relevant ERFA function that calculates greenwich sidereal time).

modelstr or None; optional

Precession (and nutation) model to use. The available ones are: - apparent: [‘IAU1994’, ‘IAU2000A’, ‘IAU2000B’, ‘IAU2006A’] - mean: [‘IAU1982’, ‘IAU2000’, ‘IAU2006’] If None (default), the last (most recent) one from the appropriate list above is used.

Returns¶

~astropy.coordinates.Longitude

Local sidereal time, with units of hourangle.

See Also¶

astropy.time.Time.earth_rotation_angle

References¶

IAU 2006 NFA Glossary (currently located at: https://syrte.obspm.fr/iauWGnfa/NFA_Glossary.html)

Notes¶

The difference between apparent sidereal time and Earth rotation angle is the equation of the origins, which is the angle between the Celestial Intermediate Origin (CIO) and the equinox. Applying apparent sidereal time to the hour angle yields the true apparent Right Ascension with respect to the equinox, while applying the Earth rotation angle yields the intermediate (CIRS) Right Ascension with respect to the CIO.

For the IAU precession models from 2000 onwards, the result includes the TIO locator (s’), which positions the Terrestrial Intermediate Origin on the equator of the Celestial Intermediate Pole (CIP) and is rigorously corrected for polar motion (except when longitude='tio' or 'greenwich').