docs: def impact_parameter(a, R, inc, ecc=0, w=0, return_occ=False):
      """a in AU, R in Rsun, inc & w in radians
      """
      b_tra = a*AU*np.cos(inc)/(R*RSUN) * (1-ecc**2)/(1 + ecc*np.sin(w))
  
      if return_occ:
          b_tra = a*AU*np.cos(inc)/(R*RSUN) * (1-ecc**2)/(1 - ecc*np.sin(w))
          return b_tra, b_occ
      else:
          return b_tra