code: def helioX(self,*args,**kwargs):
          
          out= self._orb.helioX(*args,**kwargs)
          if len(out) == 1: return out[0]
          else: return out
docs: NAME:
  
             helioX
  
          PURPOSE:
  
             return Heliocentric Galactic rectangular x-coordinate (aka "X")
  
          INPUT:
  
             t - (optional) time at which to get X (can be Quantity)
  
             obs=[X,Y,Z] - (optional) position of observer 
                           in the Galactocentric frame
                           (in kpc and km/s) (default=[8.0,0.,0.]; entries can be Quantity)
                           OR Orbit object that corresponds to the orbit
                           of the observer
                           Y is ignored and always assumed to be zero
  
             ro= (Object-wide default) physical scale for distances to use to convert (can be Quantity)
  
          OUTPUT:
  
             helioX(t) in kpc
  
          HISTORY:
  
             2011-02-24 - Written - Bovy (NYU)