Year: 1958
Type: article
Abstract: These photographic observations of positions of minor planets, which have been selected for purposes of fundamental astronomy, including correction of the proposed Catalogue of Faint Stars, are published under the heading " precise "' to indicate that they have been made and reduced with rather more attention to detail than is necessary for general measures of positions of minor planets.The plates were taken with the 8-inch wide angle camera of Yale University Observatory (Y), scale 100" to the millimetre, which was mounted here from 1954 July to 1956 September, the 13-inch standard astrograph (A), and the 9-inch camera made by Taylor, Taylor and Hobson, scale 116" to the millimetre (T).On each plate were taken four exposures separated in declination by approximately 0'-5.Guiding was performed on the planet in right ascension only, when the planet was bright enough.When the planet was too faint the guiding mechanism (Wood, 1954) was set at the appropriate speed in right ascension only and the guiding done on a star.The beginnings and endings of the exposures were recorded on a chronograph.The exposure times ranged from 40 seconds to 240 seconds.Rectangular coordinates of each image of the minor planet and six reference stars were measured on a long screw measuring machine in direct and reversed positions of the plate.The proper motions in the catalogues were used to bring the star positions to the epoch of the plate but no corrections have been applied to alter the system of the catalogues.The stars were divided into two groups and the planet's position was measured before and after the three stars of each group in each position of the plate.The measures of the first two and the last two exposures were averaged and the reduction was then performed four times, twice with each group of stars.The usual three star dependence reduction was used, including to third order terms in the differences of the equatorial coordinates.No correction which could affect the result by as much as 0"-01 has been neglected.The tabulated results give means for all four images for the separate groups of stars at the mean of the times.The differences between the results average 08-024 sec § in right ascension and 0"-32 in declination.This corresponds to probable errors for the mean of the two results from one plate of 08-010 sec 5 and 0"-14.In the case of those planets, Ceres and Juno, which have ephemerides in the Nautical Almanac the result from the first two exposures was compared with that from the last two by adding the movement computed from the ephemeris.The means of the differences so obtained were 08-017 sec 3 in right ascension and 0"-14 in declination.In this comparison the star places are used in the same way for each position and the seeming improvement in the probable errors illustrates the extent to which the results are influenced by errors in the star places.
DOI: 10.5962/p.360744
Author: William Humphrey Robertson
Institution: Harvard University
Language: English
Topic: Astro and Planetary Science
Subfield: Space and Planetary Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W4382881680