Our Astronomical Column

Abstract

PHOTOGRAPHIC MAGNITUDES OF NOVA AURIGÆ.—Astronomical Journal, No. 269, contains the results of Mr. J. M. Schaeberle's work with regard to the determination of the photographic magnitudes of stars, including also that of Nova Aurigæ. The method he has adopted differs from those used by former observers in that the photographic magnitude of a star for any exposure-time is expressed “as a function of the equivalent theoretical aperture which a standard star (Polaris in this case) would require to make the same impression on the plate in the same time.” The particular form which the expression, as obtained from this investigation, assumes enables one, after having once adopted the photographic magnitude of the standard star, to determine the theoretical photographic magnitude of any other star without any reference at all to the visual magnitude. As this method had only been applied to bright stars, the appearance of Nova Aurigæ suggested a further trial for stars of less magnitude which were visible only in large instruments. On the plates, which were each night exposed, three stars in the region of the Nova, the images of which resembled somewhat that of the Nova in form, size, and density, were selected for the sake of comparison. The magnitudes of these comparison stars were then determined by direct measurement of their images on the standard positive plate, this plate being a second positive from the original negative. The resulting photographic magnitudes for the month of February showed that the light of this new star fluctuated very considerably, confirming the visual observations.