We prove a generalization and give a new proof of a theorem of Borel-Harish-Chandra on closed orbits of linear actions of reductive groups. Consider a real reductive algebraic group G acting linearly and rationally on a real vector space V . G can be viewed as the real points of a complex reductive group G C which acts on V C := V ⊗ C. In [BHC62] it was shown that G · v ∩ V is a finite union of...