A complete description of the antipodal set of most symmetric spaces of compact type

It is known that the antipodal set of a Riemannian symmetric space of compact type G/K consists of a union of K-orbits. We determine the dimensions of these K-orbits of most irreducible symmetric spaces of compact type. The symmetric spaces we are not going to deal with are those with restricted root system \mathfrak a_r and a non-trivial fundamental group, which is not isomorphic to \mathbb Z_2 or \mathbb Z_r+1. For example, we show that the antipodal sets of the Lie groups Spin(2r+1)r≥5, E_8 and G_2 consist only of one orbit which is of dimension 2r, 128 and 6, respectively; \SO(2r+1) has also an antipodal set of dimension 2r; and the Grassmannian Gr_r,r+q(R) has a rq-dimensional orbit as antipodal set if r≥5 and r≠q>0.