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Argentina
ARGENTINA ------------------------------------------439[EXPERIENCE]

El Leoncito Observatory in Barreal

By Jazmin Agudelo for Ruta Pantera on 10/9/2025 10:25:08 AM

Imagine a sky so pristine that the stars seem within reach, a place where the silence of the cordillera is broken only by the hum of telescopes probing the universe. This is no cosmic dream—it’s the reality of the El Leoncito Astronomical Observatory, known as CASLEO, nestled within El Leoncito National Park in Barreal, San Juan Province, Argentina. Perched at 2,552 meters above sea level, this complex is not only a stronghold of astronomical science in South America but also a tourist destination inviting enthusiasts and experts to connect with the cosmos. With over 270 clear nights annually, its unique conditions make it a paradise for stargazing, rivaling international observatories. From a Visionary Idea to a Cutting-Edge Complex The origins of CASLEO trace back to the mid-1940s, shortly after the inauguration of the 1.52-meter telescope at the Bosque Alegre Astrophysical Station of the Córdoba Astronomical Observatory. The concept of a major telescope for the southern hemisphere gained momentum in 1958 when Dr. Jorge Sahade, after consultations in the United States, recommended a 2.15-meter instrument similar to the one at Kitt Peak, Arizona, with an estimated cost of $2 million. In the 1960s, scientists from Yale University confirmed the exceptional conditions of the site donated by Héctor Hilario Zamarbide, noting its clarity, low humidity, and absence of light pollution. The complex was formally established on May 10, 1983, through an agreement between the Subsecretariat of Science and Technology (SUBCYT), the National Council for Scientific and Technical Research (CONICET), the National University of La Plata (UNLP), the National University of Córdoba (UNC), and the National University of San Juan (UNSJ). Inaugurated on September 12, 1986, by President Raúl Alfonsín, it began operations on March 1, 1987. The main telescope remained stored for 20 years in La Plata before its transfer. In 1993, the area was designated a Strict Nature Reserve, and in 2002, it became part of El Leoncito National Park, spanning 70,000 hectares to protect the sky from light pollution, under Provincial Law Nº 5771. Today, CASLEO celebrates over 40 years of contributions to astronomy, with a state investment exceeding $20 million.
A Sanctuary in the Heights Located in the Calingasta Department, 40 km south of Barreal, CASLEO sits on the western slopes of the Sierra del Tontal, at the foot of the Andes. Its coordinates are 31°47′55″S 69°17′44″W, at 2,552 meters above sea level, within a 70,000-hectare Astronomical Reserve that ensures dark skies with an average of 270-300 clear nights per year. The site was chosen for its desert climate, low winds, and minimal pollution, surpassing even some international observatories in atmospheric clarity. The facilities span over 2,000 m² of covered space, with lodging capacity for 20-42 people in separate buildings for scientists and visitors. They include precision mechanics workshops, electronics, optics, and computing laboratories, a self-sustaining power plant with generators, and continuous energy systems for sensitive equipment. Additional telescopes are located on Cerro Burek, 5 km away, under international agreements. The complex is not accessible for individuals with mobility limitations due to stairs and uneven terrain. Tools to Explore the Cosmos The heart of CASLEO is the Jorge Sahade Telescope (JS), a 2.15-meter Ritchey-Chrétien reflector—the largest in Argentina—owned by UNLP, weighing 40 tons and mounted on a 15-meter concrete base. It features instruments like a photometer, spectrograph, polarimeter, and detectors for direct imaging, calibrated daily. Others include the Helen Sawyer Hogg Telescope (HSH) of 24" (0.61 m), from the University of Toronto, operational since 1997; the Solaris-4 Telescope for searching circumbinary exoplanets, part of a Polish network; the Southern Hemisphere Astrolabe (ASH), operable remotely under an agreement with Spain; and the Submillimeter Solar Telescope (SST) for studying solar flares, in collaboration with Brazil. An additional solar telescope analyzes sunspots and solar cycles, and a 35 cm MIR telescope allows outdoor observations. Maintenance includes mirror aluminizing in a vacuum chamber.

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