SOHO_EPHEMERIS(3)



NAME

     soho_ephemeris, soho_latitude, soho_longitude, soho_obs_dist
     -- positional and physical ephemeris of Sun as observed from
     SOHO


SYNOPSIS

     #include <soi_time.h>
     #include <soi_ephem.h>

     int soho_ephemeris (TIME obs_time, double *r_sun_soho,
         double *soho_lat, double *soho_lon, double *vr,
         double *vn, double *vw, TIME *mod_time)
     double soho_latitude (TIME obs_time)
     double soho_longitude (TIME obs_time)
     double soho_obs_dist (TIME obs_time)



DESCRIPTION

     soho_ephemeris interpolates the tabulated positional  ephem-
     eris  of  SOHO  to the requested observation time, returning
     the Sun--SOHO distance in  Astronomical  Units,  the  helio-
     graphic  coordinates  of SOHO in degrees, and the components
     of the SOHO heliocentric velocity in m/s.  The  normal  time
     step of the ephemeris tables is 10 minutes, so linear inter-
     polation is used.  The most recent modification time of  the
     ephemeris table is also returned.

     The    functions    soho_latitude,    soho_longitude,    and
     soho_obs_dist  simply  return  the corresponding elements of
     the ephemeris for a given time, with no status  information;
     they  are  convenience  functions to avoid having to provide
     the full set of arguments required by soho_ephemeris.


FILES

     ~CM/tables/ephemeris/summary
     /usr/local/lib/libastro.a


SEE ALSO

     solephem(3), carrington_rots(3)


DIAGNOSTICS

     Return values:

     0    normal
     1    requested observation time within one time step beyond last entry in
          table
     -1   requested observation time outside range of table
     -2   ephemeris table could not be read

     If the  return  value  is  negative,  the  ephemeris  values
     returned  are  those  for the Earth (calculated) rather than
     SOHO.  Values for times within one  time-step  of  the  last
     tabulated value are simply continued, not extrapolated.


BUGS

     There is no provision for gaps in the table.  Since gaps are
     marked by zero values for all ephemerides, the function will
     return garbage values within a time step  of  any  gap.   No
     warning is returned.

     The ephemeris values change discontinuously at  the  end  of
     the tabulated range, but with a warning at least.