Detailed Description

XLAL routines for computing the sidereal time.

Author: Creighton, J., and Cannon, K.

Synopsis

#include <lal/Date.h>

Prototypes
REAL8	XLALGreenwichSiderealTime (const LIGOTimeGPS *gpstime, REAL8 equation_of_equinoxes)
	Returns the Greenwich Sidereal Time IN RADIANS corresponding to a specified GPS time. More...

REAL8	XLALGreenwichMeanSiderealTime (const LIGOTimeGPS *gpstime)
	Convenience wrapper, calling XLALGreenwichSiderealTime() with the equation of equinoxes set to 0. More...

LIGOTimeGPS *	XLALGreenwichMeanSiderealTimeToGPS (REAL8 gmst, LIGOTimeGPS *gps)
	Inverse of XLALGreenwichMeanSiderealTime(). More...

LIGOTimeGPS *	XLALGreenwichSiderealTimeToGPS (REAL8 gmst, REAL8 equation_of_equinoxes, LIGOTimeGPS *gps)
	Convenience wrapper of XLALGreenwichMeanSiderealTimeToGPS(), adjusting the input by the equation of equinoxes. More...

Function Documentation

◆ XLALGreenwichSiderealTime()

REAL8 XLALGreenwichSiderealTime	(	const LIGOTimeGPS *	gpstime,
		REAL8	equation_of_equinoxes
	)

Returns the Greenwich Sidereal Time IN RADIANS corresponding to a specified GPS time.

Aparent sidereal time is computed by providing the equation of equinoxes in units of seconds. For mean sidereal time, set this parameter to 0.

This function returns the sidereal time in radians measured from the Julian epoch (current J2000). The result is NOT modulo 2 pi.

Inspired by the function sidereal_time() in the NOVAS-C library, version 2.0.1, which is dated December 10th, 1999, and carries the following references:

Aoki, et al. (1982) Astronomy and Astrophysics 105, 359-361. Kaplan, G. H. "NOVAS: Naval Observatory Vector Astrometry Subroutines"; USNO internal document dated 20 Oct 1988; revised 15 Mar 1990.

See http://aa.usno.navy.mil/software/novas for more information.

Note: rather than maintaining this code separately, it would be a good idea for LAL to simply link to the NOVAS-C library directly. Something to do when we have some spare time.

Definition at line 62 of file XLALSiderealTime.c.

◆ XLALGreenwichMeanSiderealTime()

REAL8 XLALGreenwichMeanSiderealTime ( const LIGOTimeGPS * gpstime )

Convenience wrapper, calling XLALGreenwichSiderealTime() with the equation of equinoxes set to 0.

Definition at line 134 of file XLALSiderealTime.c.

◆ XLALGreenwichMeanSiderealTimeToGPS()

LIGOTimeGPS* XLALGreenwichMeanSiderealTimeToGPS	(	REAL8	gmst,
		LIGOTimeGPS *	gps
	)

Inverse of XLALGreenwichMeanSiderealTime().

The input is sidereal time in radians since the Julian epoch (currently J2000 for LAL), and the output is the corresponding GPS time. The algorithm uses a naive iterative root-finder, so it's slow.

Definition at line 148 of file XLALSiderealTime.c.

◆ XLALGreenwichSiderealTimeToGPS()

LIGOTimeGPS* XLALGreenwichSiderealTimeToGPS	(	REAL8	gmst,
		REAL8	equation_of_equinoxes,
		LIGOTimeGPS *	gps
	)

Convenience wrapper of XLALGreenwichMeanSiderealTimeToGPS(), adjusting the input by the equation of equinoxes.

Definition at line 174 of file XLALSiderealTime.c.