docs: def distancemodulus(d):
      """Returns distance modulus given d in parsec.
      """
      if type(d)==Quantity:
          x = d.to('pc').value
      else:
          x = d #assumed to be pc
  
      if np.size(x)>1:
          d = np.atleast_1d(x)
      return 5*np.log10(x/10)