to extend their catalogue of stellar positions to the Southern Hemisphere. The USNO returned that telescope to Washington following the completion of its project in 1974. At about the same time Columbia University withdrew from the YCSO corporation it became the Yale Southern Observatory, Inc. on January 23, 1975. About two years earlier, the University of Cuyo had split into several regionally based units. The one based in San Juan became known as the National University of San Juan (UNSJ) and it assumed the administration of the OAFA and partnership with the YCSO and then the YSO. In 1990 the El Leoncito Observatory was renamed The Dr. Carlos U. Cesco Observatory on the occasion of the 25th anniversary of the beginning of observations, in honour of Dr. Cesco's many contributions to the founding and operation of the Observatory. During the period 1974-1983, El Leoncito was run by OAFA under terms of an agreement signed by the OAFA and the YSO. In 1983 a new ten-year agreement was negotiated that allowed the Southern Sky survey to be repeated, and this was again extended for another ten-year period in 1993. Around 1987, Eastman Kodak terminated the production of the photographic plates used in the survey after only one-third of the second epoch photography had been completed; in 1997 a CCD detector system was installed on the telescope to replace the photographic plates. Telescopes The principal telescope of EACUC is a double astrograph consisting of two lenses each 20-inches (50.8 cm) in diameter, one designed for blue light and the other for yellow light. The lenses focus the light separately onto two photographic plates with dimensions of 17×17 inches (43×43 cm). The photographic plates are purchased in the U.S., shipped to Argentina, exposed in the telescope, developed, and then shipped back to the U.S. In New Haven, Connecticut, the plates are measured with a precision measuring machine. See also Leoncito Astronomical Complex Argentine National Observatory List of astronomical observatories References External links OAFA – The Yale Southern Observatory Facultad de Ciencias Exactas Físicas y Naturales in Spanish Astronomical observatories in Argentina Minor-planet discovering observatories Buildings and structures in San Juan Province, Argentina