Intrinsic volumes and polar sets in spherical space

Abstract

Abstract. For a convex body of given volume in spherical space, the total invariant measure of hitting great subspheres becomes minimal, equivalently the volume of the polar body becomes maximal, if and only if the body is a spherical cap. This result can be considered as a spherical counterpart of two Euclidean inequalities, the Urysohn inequality connecting mean width and volume, and the Blaschke-Santalo ́ inequality for the volumes of polar convex bodies. Two proofs are given; the first one can be adapted to hyperbolic space.