8. (Sichuan Province) Given a regular tetrahedron inscribed in a sphere with a radius of 3, and the side length of the base is $2 \sqrt{3}$, then the angle between the side edge of the tetrahedron and the base is $\qquad$ .
8. $\operatorname{arctg} \frac{3+\sqrt{5}}{2}$ or $\operatorname{arctg} \frac{3-\sqrt{5}}{2}$.