2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/203787The past quasi-local horizons in vacuum Robinson-Trautman spacetimes are described. The case of a null (non-expanding) horizon is discussed. It is shown that the only Robinson-Trautman space-time admitting such a horizon with sections diffeomorphic to S_2 is the Schwarzschild space-time. Weakening this condition leads to the horizons of the C-metric. Properties of the hypersurface r=2m for finite retarded time u are examined.11pGeneral Relativity and Quantum Cosmologytext