  We prove an effective equidistribution result for periodic orbits of
semisimple groups on congruence quotients of an ambient semisimple group. This
extends previous work of Einsiedler, Margulis and Venkatesh. The main new
feature is that we allow for periodic orbits of semisimple groups with
nontrivial centralizer in the ambient group. Our proof uses crucially an
effective closing lemma from work with Lindenstrauss, Margulis, Mohammadi, and
Shah.
