Proper Motions of 25,000 Stars

Abstract

IN 1906 Kapteyn published his “Plan of Selected Areas“to bring together the various observational elements necessary for a more complete knowledge of the structure of the system of the stars. To obtain data for the fainter stars (position, proper motion, magnitude, spectrum, radial velocity, and so on), he proposed that samples of 206 areas uniformly distributed over the sky should be completely investigated, and work was apportioned to different observatories. Rambaut undertook the determination of the proper motions over fields of 40′ x40′, 50′ x50′, 60′ x60′, depend-ing on galactic latitude, for the 115 areas from the equator to the north pole. Kapteyn's proposal was that exposures should be made sufficient to obtain stars to a definite magnitude, the plates carefully stored, and re-exposed ten years later with their centres displaced slightly. This method has the disadvantage that at the second exposure, if clouds came up, the necessary limit of magnitude might not be reached. The plan was modified by taking the second exposure on a separate plate, through the glass, and measuring the displacements by placing the plates face to face. Rambaut carried on the work from 1907 until 1923, and it has been completed under his successor's direction. The difficulties attending long exposures in the climate of Great Britain are considerable, and although the aggregate exposure time on which the proper motions depend has been only 450 hours, “it has taken 24 years of unremitting effort to achieve this modest score”.

The Radcliffe Catalogue of Proper Motions in the Selected Areas 1 to 115.

Compiled by Dr. H. Knox-Shaw and H. G. Scott Barrett. Published by Order of the Radcliffe Trustees. Pp. xlviii + 352. (London: Oxford University Press, 1934.) n.p.