Félix Aguilar Observatory, Astronomical observatory in El Leoncito National Park, Argentina

The Félix Aguilar Observatory is an astronomical research facility located in the eastern Andes foothills at 2348 meters elevation in San Juan Province. It houses specialized telescopes with two 20-inch lenses that capture different wavelengths of light for detailed astronomical measurements and stellar study.

The observatory was established in 1953 and named after Félix Aguilar, director of the La Plata Astronomical Observatory. In 1960 Yale University secured 750,000 dollars from the Ford Foundation to build a southern station at El Leoncito, near Barreal, at about 2,400 m in the eastern Andes foothills. The first survey of the southern sky ran from 1965 to 1974 with NSF funding. In 1990 the El Leoncito station was renamed for Carlos Ulrrico Cesco on the 25th anniversary of the start of observations.

The National University of San Juan manages the observatory through its School of Physical and Natural Sciences, conducting research and organizing educational programs.

The site sits in a mountain area with thin air, making it ideal for observations of exceptionally clear skies. Visitors should prepare for high altitude conditions, changeable weather, and limited facilities on location.

The main-belt asteroid 3083 OAFA was named after this observatory; the official naming citation was published on 21 November 1991. In 2025 Argentina suspended construction of the China Argentina Radio Telescope here over U.S. concerns about dual-use.