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include <math.h>
# AST_VROTATE -- Radial velocity component of the observer relative to
# the center of the Earth due to the Earth's rotation.
procedure ast_vrotate (ra, dec, epoch, latitude, longitude, altitude, v)
double ra # Right Ascension of observation (hours)
double dec # Declination of observation (degrees)
double epoch # Epoch of observation (Julian epoch)
double latitude # Latitude (degrees)
double longitude # Latitude (degrees)
double altitude # Altitude (meters)
double v # Velocity (km / s)
double lat, dlat, r, vc, lmst, ast_mst()
begin
# LAT is the latitude in radians.
lat = DEGTORAD (latitude)
# Reduction of geodetic latitude to geocentric latitude (radians).
# Dlat is in arcseconds.
dlat = -(11. * 60. + 32.743000d0) * sin (2 * lat) +
1.163300d0 * sin (4 * lat) -0.002600d0 * sin (6 * lat)
lat = lat + DEGTORAD (dlat / 3600.)
# R is the radius vector from the Earth's center to the observer
# (meters). Vc is the corresponding circular velocity
# (meters/sidereal day converted to km / sec).
# (sidereal day = 23.934469591229 hours (1986))
r = 6378160.0d0 * (0.998327073d0 + 0.00167643800d0 * cos (2 * lat) -
0.00000351d0 * cos (4 * lat) + 0.000000008d0 * cos (6 * lat)) +
altitude
vc = TWOPI * (r / 1000.) / (23.934469591229d0 * 3600.)
# Project the velocity onto the line of sight to the star.
lmst = ast_mst (epoch, longitude)
v = vc * cos (lat) * cos (DEGTORAD (dec)) *
sin (DEGTORAD ((ra - lmst) * 15.))
end
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