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LALPulsar 7.1.1.1-ea7c608
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Header GetEarthTimes.h

Detailed Description

Computes the next sidereal midnight and autumnal equinox.

Author
Creighton, T. D.

Prototypes

int XLALGetEarthTimes (const LIGOTimeGPS *tepoch, REAL8 *tMidnight, REAL8 *tAutumn)
 This function takes a GPS time from tepoch and uses it to assign tAutumn and tMidnight, which are REAL8 representations of the time in seconds from tepoch to the next autumnal equinox or sidereal midnight, respectively. More...
 

Function Documentation

◆ XLALGetEarthTimes()

int XLALGetEarthTimes ( const LIGOTimeGPS tepoch,
REAL8 tMidnight,
REAL8 tAutumn 
)

This function takes a GPS time from tepoch and uses it to assign tAutumn and tMidnight, which are REAL8 representations of the time in seconds from tepoch to the next autumnal equinox or sidereal midnight, respectively.

Algorithm

The routine first computes the Greenwich mean sidereal time at tepoch using XLALGreenwichMeanSiderealTime(). The next sidereal midnight (at the Prime Meridian) is simply 86400 seconds minus that sidereal time.

Next the routine computes the time of the next autumnal equinox. The module contains an internal list of GPS times of autumnal equinoxes from 1992 to 2020, given to the nearest minute. If the specified time tepoch is after the 2020 autumnal equinox, or more than a year before the 1992 equinox, then the next equinox is extrapolated assuming exact periods of length LAL_YRSID_SI.

It is up to the user to choose a tepoch that is close to the actual times that are being considered. This is important, since many computations use a REAL8 time variable whose origin is the time tepoch. If this is too far from the times of interest, the REAL8 time variables may suffer loss of precision.

Uses

REAL8 XLALGreenwichMeanSiderealTime(const LIGOTimeGPS *gpstime)

Definition at line 76 of file GetEarthTimes.c.