2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/34848We show that static metrics solving vacuum Einstein equations (possibly with a cosmological constant) are one-sided analytic at non-degenerate Killing horizons. We further prove analyticity in a two-sided neighborhood of "bifurcate horizons". It is a pleasure to dedicate this work to Prof. Staruszkiewicz, on the occasion of his 65th birthday.latex2e, 9 pages in A4, minor wording improvementsGeneral Relativity and Quantum Cosmologytext