Abstract
ANNALS OF HARVARD COLLEGE OBSERVATORY.—We have received Part 2 of vol. xiii. of the Annals of Harvard College Observatory, containing zone observations with the transit wedge photometer attached to the 15-inch equatorial. These observations were undertaken in order to extend our knowledge of the relative brightness of the fainter stars, and to determine the scales of magnitude employed in the estimates of certain observers, as compared with magnitudes as obtained by means of the meridian photometer. These zone observations were not, however, made with the meridian photometer, but with an adaptation of Prof. Pritchard's wedge photometer, which had been devised by Prof. Pickering. Instead of slipping the wedge along by hand, the telescope and wedge are fixed, and the star is carried from the thin part of the wedge towards the thick by the diurnal motion. An occulting bar is fixed near the thin edge, and the interval between the time of the occultation of a star by the bar, and its extinction by the wedge, is proportional to the magnitude of the star on the assumption of a uniform scale of absorption throughout the wedge. In this way the relative magnitudes, right ascensions, and (by estimating the point on the bar where they are occulted) the declinations of a number of stars were determined with great rapidity, and the results made comparable with magnitudes observed with the meridian photometer by the observation of a sufficient number of standard stars. The observations were made in three zones each 10′ in breadth, and lying immediately to the south of N. Decl. 1°, 50°, and 55°, the first zone being part of those observed more than twenty years ago by Prof. Bond, and the other two being situated on the north and south margins of the zone recently revised with the Harvard College meridian circle. A comparison of the D. M. magnitudes between the 7th and 9th with magnitudes as determined in the preceding manner show that the former closely correspond to the magnitudes derived from the mean of the three zones, the zone at 1° N. giving a value of about two-tenths of a magnitude less than the other two. But for fainter stars the three zones are in close accordance with each other, whilst the D.M. values give in comparison too small a magnitude, the difference increasing rapidly until 9.5 magnitude in the Durchmusterung is found to correspond to 10.5 with the wedge photometer. Prof. Bond's scale, on the other hand, corresponds fairly to that of the photometer from 7.0 magnitude up to 11.0, but beyond gives magnitudes which are too large, so that his 13.5 magnitude corresponds to about 12.5 of the wedge.
Article PDF
Rights and permissions
About this article
Cite this article
Our Astronomical Column . Nature 37, 475 (1888). https://doi.org/10.1038/037475a0
Issue Date:
DOI: https://doi.org/10.1038/037475a0