code: def ConvertRADecToThetaPhi(RA, Dec, GPSTime): 
       
                  
      # Get Greenwich mean sidereal time corresponding to GPSTime 
      GMST = ComputeGMST(GPSTime) 
              
      # RA -> Phi
      Phi = RA - GMST
              
      # Dec -> Theta
      Theta = np.pi/2. - Dec
              
      return Theta,Phi
docs: ConvertRADecToThetaPhi - function to convert right ascension and 
          declination of an astronomical source to theta and phi in the geocentric 
          coordinate system. 
              
          RA - Right ascension of source. 
          Dec - Declination of source. 
          GPSTime - GPS time that the GW signal from the source reached the
  		  geocenter. 
                  
          Returns Theta - Polar angle of source's sky position in geocentric 
                          coordinates. 
                  Phi - Azimuthal angle of source's sky position in geocentric 
                        coordinates. 
              
          Sarah Gossan 2012.