Our Astronomical Column

Abstract

THE NEBULA IN ORION.—M. Tisserand, Director of the Observatory at Toulouse, commenced on Feb. 17 of the present year, a close examination of the small stars in the vicinity of the trapezium in the great nebula of Orion, with the Foucault telescope of om80 aperture, which had been completely mounted at the beginning of the same month. To facilitate the study of this region, which it is intended shall form part of the.work with this fine instrument, a chart was prepared on a large scale containing the 155 stars, the positions of which relatively to θl Orionis, were determined by M. O. Struve (Observations de la Grande Nebuleuse d'Orion in the St. Petersburg Memoirs, vol. v.); of these 155 stars it may be mentioned that 150 occur in Sir John Herschel's list in the volume of observations made at the Cape of Good Hope. Especial attention was directed at Toulouse during the few week.? that the nebula could be observed in the last season, to the stars which M. O. Struve had indicated as variable. The star n (An - 7 3, AS 276) which is not in Herschel's catalogue, was noted on Feb. 17 and 21 at the extreme limit of visibility: on following days, when the sky was more transparent, it could not be discerned; at maximum according to Struve this star is of the twelfth magnitude, the smallest star which can be distinctly seen in the Pulkowa refractor being considered 13.5-a very different scale of magnitude, it will be remarked, from that of Bessel; No. 78 (Ac … +345, AS … + 97) varying, according to Struve, from 12.5 to invisibility, was not discerned.; No. 75 (Aa … + 213, AS … + 39/2) was 14-15 on March 14; Tisserand found No. V. of the Pulkowa list (A a … + 3783, AS … + 663) extremely faint on Feb. 24, and quite invisible subsequently, whence he concludes this star to be also variable, and that its non-insertion by Herschel may have arisen from its being at a minimum at the epoch of his observations.