code: def _true_anom_to_phase(true_anom, period, ecc, per0):
      
      phshift = 0
  
      mean_anom = true_anom - (ecc*sin(true_anom))*u.deg
  
      Phi = (mean_anom + per0) / (360*u.deg) - 1./4
  
      # phase = Phi - (phshift - 0.25 + per0/(360*u.deg)) * period
      phase = (Phi*u.d - (phshift - 0.25 + per0/(360*u.deg)) * period)*(u.cycle/u.d)
  
      return phase
docs: TODO: add documentation