Félix Aguilar Observatory: Foundation and Southern-Sky Collaboration

Félix Aguilar Observatory was inaugurated in San Juan, Argentina, on 28 September 1953, as part of the then National University of Cuyo. Its origins lay in geographical engineering education: Carlos Ulrico Cesco and other teachers needed to train students in precise astronomical and geographical measurement, later developing the teaching facilities into a research institution. It was named for Félix Aguilar, the astronomer and geodesist born in San Juan.

The provincial government provided five hectares in Chimbas, and the San Juan Reconstruction Committee undertook construction. Architect Federica Rosenfeld designed the main building with classrooms, a library, offices and a basement clock room. An eastern dome housed an equatorial telescope; separate buildings accommodated a transit instrument and resident staff.

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The initial main telescope was a Steinheil refractor with an aperture of 175 millimeters and a focal length of 315 centimeters, previously owned by amateur astronomer Juan Carullo of Mendoza. The equipment also included a Bamberg transit instrument. Riefler pendulum clocks were the main timekeepers, supplemented by sidereal and mean solar time clocks to support measurements of observation times and directions.

Cesco’s 1954 report describes specific responsibilities. Bernhard Dawson observed lunar occultations and trained geographical engineering students. Juan José Nissen organized computing staff for planned asteroid-orbit and eclipsing-binary calculations. Juan Campora was already calculating the orbit of Pallas, while José Augusto López used the transit instrument to test azimuth determination away from the meridian.

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In 1959, Cesco established contact with Dirk Brouwer at Yale and Jan Schilt at Columbia, leading to surveys for a southern observing site. El Leoncito, in the Calingasta region, was selected at a location separate from the Chimbas headquarters. The University of Cuyo and the Yale–Columbia Southern Observatory signed a cooperation agreement in 1962.

The new station was inaugurated on 31 March 1965. Its double astrograph had already undergone trial exposures: Arnold Klemola and Cyril Jackson obtained the first focusing plate during the night of 27–28 October 1964. Initially, the station maintained its own staff and administration while working closely with Aguilar Observatory. The 1965 date therefore refers to the high-altitude station’s inauguration.

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The Southern Proper Motion program used distant galaxies as references to measure changes in stars’ apparent positions over many years, studying the Milky Way’s structure and motion. The station’s 51-centimeter double astrograph mounted two telescope tubes together for blue and visual images. Each plate, approximately 43 centimeters square, covered a field about 6.3 degrees square, with overlaps between neighboring fields.

Photographic observations combined two-hour and two-minute exposures. An objective grating produced diffraction images of bright stars, allowing brighter stars and faint galaxies to be tied into the same measurement system. First-epoch photography continued from 1965 to 1979. Proper motions were derived by reobserving the same fields later and comparing positions across epochs.

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While the long-term proper-motion program was still accumulating its initial images, the plates yielded other research. Klemola systematically inspected blue photographs and assembled 44 candidate southern galaxy groups or clusters for further investigation. In 1969, he published their positions, morphology and membership characteristics.

The list supplied targets for subsequent observation. Klemola explained that apparent groupings on the sky had not yet established physical associations, and that positions and brightnesses were largely estimated visually. Wide-field plates could thus serve another purpose alongside recording the initial epoch of stellar motions: identifying concrete targets for galaxy research.

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In the 1970s, the National University of San Juan took over Aguilar Observatory and the collaboration was reorganized. A 1974 agreement increased Aguilar’s participation in the Southern Proper Motion program, including facilities maintenance and staffing, while Yale continued to handle instrument upgrades. Chimbas and El Leoncito consequently developed a closer operational relationship.

The early glass plates preserved the starting epoch needed for long-term measurements. Published in 2011, the fourth Southern Proper Motion catalog combined photographic material with later digital observations and contained data for more than 100 million stars and galaxies. It depended on decades of repeated observations and data processing.

References: [2] [3]