caput.astro.observer#
Time and ephemeris calculations for a local observer.
Local Time Utilities#
Routines are provided through the location-aware class Observer.
This class can be used to calculate Local Stellar Angle (LSA), and the Local Stellar Day (LSD). LSA is an equivalent to the Local Sidereal Time based around the Earth Rotation Angle instead of the Greenwich Sidereal Time. This is defined as:
where \(\theta\) is the Earth Rotation Angle, and \(\lambda\) is the longitude. Local Stellar Day counts the stellar days (i.e. the number of cycles of LSA) that have occured since a given start epoch. This means that the fractional part is simply the LSA rescaled., with the integer part the number of stellar days elapsed since that epoch. This requires the specification of the start epoch, which is determined from a given UNIX time, the code simply picks the first time \(\mathrm{LSA} = 0\) after this time.
Note that the quantities LSA and LSD are not really used elsewhere. However, the concept of a Stellar Day as a length of time is well established (IERS constants), and the Stellar Angle is an older term for the Earth Rotation Angle (NFA Glossary).
Classes#
Time calculations for a local observer. |