Manuel Foster Observatory, Historical astronomical observatory in Cerro San Cristóbal, Chile

The Manuel Foster Observatory stands on the middle rise of Cerro San Cristóbal, beside the summit shrine, at about 262 m above Santiago. Its main instrument is a Cassegrain reflector with a 0.93 m mirror on an equatorial mount, housed in a rotating steel dome built by Warner & Swasey. The mount came from Fulton Engine Works and the optics from Brashear.

The facility was originally built in 1903 as Mills Observatory and operated for decades collecting astronomical data. In 1928, Manuel Foster Recabarren took ownership of the establishment, leading to the name change under which it continues to operate today.

The observatory's name honours Manuel Foster Recabarren, the lawyer who bought the equipment from Lick Observatory in 1929 and gave it to the Pontificia Universidad Católica de Chile. Since June 2022 it has opened to visitors year-round, after earlier opening only on the Día del Patrimonio Cultural. In 2019 Tryo Teatro Banda premiered the play "El observatorio del Cerro Tupahue" about the American scientists who installed it.

The site is accessible through the Santiago Metropolitan Park, which has multiple entry points and pathways leading to the facility. Visitors should prepare for an uphill walk and wear comfortable shoes, as the terrain can be steep and uneven.

The facility contributed to international research aimed at understanding solar motion through space using observations from the southern hemisphere. Astronomers gathered critical data here that advanced their knowledge of the Sun's position in the cosmos.