| El Leoncito Astronomical Complex | |
| Organization: | National Scientific and Technical Research Council |
| Code: | 829 |
| Location: | San Juan Province, Argentina |
| Altitude: | 2483m (8,146feet) |
| Telescope1 Name: | Jorge Sahade Telescope |
| Telescope1 Type: | 2.2 m reflector |
| Telescope2 Name: | Solar Submillimeter Telescope |
| Telescope2 Type: | 1.5 m radio telescope |
| Telescope3 Name: | Helen Sawyer Hogg Telescope |
| Telescope3 Type: | 0.6 m reflector |
| Telescope4 Name: | Astrograph for the Southern Hemisphere |
| Telescope4 Type: | 0.5 m reflector |
| Telescope5 Name: | Horacio Ghielmetti Telescope |
| Telescope5 Type: | 0.4 m reflector |
The El Leoncito Astronomical Complex (Spanish: Complejo Astronómico El Leoncito - CASLEO) is an astronomical observatory in the San Juan Province of Argentina. CASLEO is one of two observatories located within El Leoncito National Park, which is in a part of the country which rarely sees cloud cover. The other facility in the park is the Carlos U. Cesco Astronomical Station of the Félix Aguilar Observatory. CASLEO was established in 1983 by an agreement between National Scientific and Technical Research Council (CONICET) of Argentina, the Ministry of Science, Technology and Innovation (MINCYT) of Argentina, the National University of San Juan (UNSJ), the National University of La Plata (UNLP), and the National University of Córdoba (UNC). The facility was dedicated in 1986 and regular observations began in 1987.
CASLEO's telescopes are located in two separate areas within the El Leoncito Park. The Jorge Sahade and Submillimeter telescopes are at the main site on the edge of the Pampa de la Ciénaga del Medio, along with support facilities. The Helen Sawyer Hogg telescope, Ghielimetti telescope, and the Astrograph for the Southern Hemisphere are located on Cerro Burek, approximately 1.6abbr=onNaNabbr=on to the northeast and 85m (279feet) higher. Separating the areas is the Arroyo El Leoncito, which flows west into the Barreal Blanco in the Pampa de El Leoncito. The driving distance between the two sites is approximately 7km (04miles).