code: def distance(pos0, pos1):
      
      r0, pa0 = pos0
      #logging.debug('r0={}, pa0={} (from {})'.format(r0, pa0, self))
      ra0 = r0*np.sin(pa0*np.pi/180)
      dec0 = r0*np.cos(pa0*np.pi/180)
  
      r1, pa1 = pos1
      #logging.debug('r1={}, pa1={} (from {})'.format(r0, pa0, other))
      ra1 = r1*np.sin(pa1*np.pi/180)
      dec1 = r1*np.cos(pa1*np.pi/180)
  
      dra = (ra1 - ra0)
      ddec = (dec1 - dec0)
      return np.sqrt(dra**2 + ddec**2)
docs: distance between two positions defined by (separation, PA)