'Vector norm.
The norm is the standard Frobenius norm, i.e., the square root of the
sum of the squares of all components with non-angular units.  For
spherical coordinates, this is just the absolute value of the distance.
Returns
norm : `astropy.units.Quantity`
Vector norm, with the same shape as the representation.'

def norm(self):

    return np.abs(self.distance)
