Eigenvalues of $-y''+x^2y$

Question

I need to find the eigenvalues of $-y''+x^2y$, that is, the values of $\lambda $ such that the equation

$$-y''+(x^2-\lambda )y=0$$ has solutions differents of $0$ in the interval $[0, \pi] $ with $y (0)=y (\pi)=0$. Can you help me, please?.