The Palomar–Leiden survey was a collaborative effort between astronomical institutions to study minor planets with visual magnitudes greater than 20. This was intended as an extension of the Yerkes–McDonald asteroid survey conducted in 1950–1952 by Gerard Kuiper, which was limited to magnitude 16. The Palomar–Leiden survey used photographic plates taken by the Lunar and Planetary Laboratory in Arizona with the 48-inch Schmidt camera at Palomar Observatory in 1960. As each minor planet was discovered, the orbital elements were computed at the Cincinnati Observatory. All other aspects of the program, including analysis of the photographs, were to be conducted at Leiden Observatory. This survey was initiated by G. Kuiper in 1961.
This survey only covered a portion of the ecliptic about the vernal equinox, with the target areas selected to minimize the number of background stars. A total of 130 photographic plates were taken during September and October 1960, with each plate spanning 35.6 × 35.6 cm having and a limiting magnitude of 20.5. The observed region covered an area of 36° × 18°. The Zeiss blink comparator from the Heidelberg Observatory was adapted to perform blink comparison of the plates. This resulted in the discovery of a large number of asteroids; typically 200–400 per plate. A subset of these objects had sufficient data to allow orbital elements to be computed. The mean error in their positions was as small as 0.6″, which corresponded to 0.009 mm on the plates. The resulting mean error in magnitude estimation was 0.19.
Analysis of the data showed gaps at 1:3 and 2:5 orbital resonances with Jupiter. Asteroids belonging to the Hungaria, Hilda and trojan groups were identified. The Palomar–Leiden survey discovered five new asteroid families. A small extension of the survey was reported in 1984, adding 170 new objects for a combined total of 2,403. A Palomar–Leiden trojan survey was performed in 1977, resulting in the discovery of 26 Jupiter trojans. In total, there were 3 Jupiter Trojan Surveys, designated T-1, T-2, and T-3, which discovered 3570 asteroids.
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