source: trunk/MagicSoft/slalib/rverot.c@ 9472

Last change on this file since 9472 was 731, checked in by tbretz, 24 years ago
*** empty log message ***
  • Property svn:executable set to *
File size: 1.4 KB
Line 
1#include "slalib.h"
2#include "slamac.h"
3float slaRverot ( float phi, float ra, float da, float st )
4/*
5** - - - - - - - - - -
6** s l a R v e r o t
7** - - - - - - - - - -
8**
9** Velocity component in a given direction due to Earth rotation.
10**
11** (single precision)
12**
13** Given:
14** phi float latitude of observing station (geodetic)
15** ra,da float apparent RA,Dec
16** st float local apparent sidereal time
17**
18** phi, ra, dec and st are all in radians.
19**
20** Result:
21** Component of Earth rotation in direction ra,da (km/s)
22**
23** Sign convention:
24** The result is +ve when the observer is receding from the
25** given point on the sky.
26**
27** Accuracy:
28** The simple algorithm used assumes a spherical Earth, of
29** a radius chosen to give results accurate to about 0.0005 km/s
30** for observing stations at typical latitudes and heights. For
31** applications requiring greater precision, use the routine
32** slaPvobs.
33**
34** Last revision: 9 April 1998
35**
36** Copyright P.T.Wallace. All rights reserved.
37*/
38
39#define ESPEED 0.4655 /* Nominal mean sidereal speed of Earth equator
40 in km/s (the actual value is about 0.4651) */
41
42{
43 return (float) ( ESPEED * cos ( (double) phi ) *
44 sin ( (double) ( st - ra ) ) *
45 cos ( (double) da ) );
46}
Note: See TracBrowser for help on using the repository browser.