2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/132672It is well known that the interior of a constant density spherical star is conformally flat. In this paper we obtain the coordinate system in which the conformal flatness of the metric manifests itself. In a similar way, we also construct such coordinates for Robertson Walker metric.13 pages. Figure 1 in page 7 and Figure 2 in page 13General Relativity and Quantum Cosmologytext