function sidtim, jd
;
; Given a scalar or array of Julian Day Numbers (& fraction), return
; the corresponding apparent sidereal time(s) at Greenwich.
;
; B. Knapp, 2001-02-15
;
; RCS Data:
;
; $Header$
;
; $Log$
;
; Print usage?
  n = n_elements( jd )
  if n eq 0 then begin
     print, ' '
     print, ' Given a scalar or array of Julian Day Numbers (& fraction),'
     print, ' this function returns the corresponding apparent sidereal'
     print, ' time(s) at Greenwich (in degrees).'
     print, ' '
     print, '     st = sidtim( jd )'
     return, ' '
  endif
;
; Use 32-bit or 64-bit shareable object library?
  mbits = ((!version.release ge 5.4) ? !version.memory_bits : 32)
  dll = getenv('bgkroot')+string(mbits,"('/lib/astron',i2,'.so')")
;
; Define output and then call the Fortran subroutine
  jd_loc = double( jd )
  st = dblarr( n )
  result = call_external( dll, 'sidtim_arg_', n, jd_loc, st )
;
; Return scalar or array, according to argument jd
  if (size( jd ))[0] eq 0 then $
     return, st[0] $
  else $
     return, st
  end