In 1951, the National Astronomical Observatory of Tacubaya, operated by the National University (UNAM,) was moved to Tonantzintla, to the same hill where the National Astrophysical Observatory (OANTon), operated by the Ministry of Public Education, was located. This telescope has an much older history, since it participated, precisely, in the Carte du Ciel project, which sought to obtain an image of the entire sky.