The nuclear electric quadrupole moment is a parameter which describes the effective shape of the ellipsoid of nuclear charge distribution. A non-zero quadrupole moment Q indicates that the charge distribution is not spherically symmetric. By convention, the value of Q is taken to be positive if the ellipsoid is prolate and negative if it is oblate. but i don't understand is that the real meaning of the shape, in my view, the prolate ellipsoid and oblate ellipsoid is the same, because if it represents the real shape of nucleus, we can change the coordinate ,then the oblate changes into oblate.or we can roate the nucleus and also can get the same result. so what's my fault?