DELTA_V(3)



NAME

     delta_v(3), delta_p(3)


SYNOPSIS

     double delta_v(time,ephem,x,y)
     TIME time;
     double ephem[];
     double x,y;

     double delta_p(time,rsun,x0,y0,x1,y1)
     TIME time;
     double rsun, x0, y0, x1, y1;


DESCRIPTION

     Collection of functions to compute various solar  coordinate
     changes and observational corrections.

     Deltav is used in conjunction with solephem(3) to  find  the
     correction to an observed velocity on the sun (in m/s).  The
     sign is such that:
          V_actual = V_obs + deltav
     The array "ephem" must have been initialized  for  the  time
     given in a prior call of solephem.  x and y are the position
     in arc-secs from disk center with y positive to north on the
     sun,  and  x  positive to the west.  V is positive away from
     the observer.  see Howard and Harvey, Solar Phys.  12,  p.23
     (1970)  and  solephem(3).   Several  auxillary (and probably
     useful) quantities are returned in ephem:
          ephem[20]: sub-solar angle of x,y (arc on surface)
          ephem[21]: longitude W from disk center
          ephem[22]: latitude N from solar equator
          ephem[23]: disk distance to x,y (0-1 on disk)
          ephem[24]: secant of zenith angle
          ephem[25]: sin longitude (sin(e[21]))
          ephem[26]: sin latitude (sin(e[22]))

          all angles in radians

     Delta_p finds the position angle difference between the  two
     points  on the disk described by x0,y0 and x1,y1 in units of
     rsun.  If x0, y0 are 0.0 then the normal position angle will
     be  found.   Position angles are measures from north through
     east.  Delta_p returns values in the range:
          -pi < delta_p <= pi



FILES

     source: /usr/src/local/astro/
     use: -lastro on ld call


SEE ALSO

     solephem(3)


DIAGNOSTICS

     Delta_v returns missing in e if x,y is off the disk.


BUGS

     Delta_v: Longitude is returned as 0.0  if  |latitude|  >  90
     degrees.