Our Astronomical Column.

Abstract

THE SPECTRUM OF BROOKS'S COMET, 1911.—Some excellent spectrograms of comet 1911c are reproduced and their special features discussed by MM. de la Baume Pluvinel and Baldet in the September number of L'Astronomie. The spectrographs employed were mounted at the Juvisy Observatory, and an examination of the complete series of plates shows very markedly the spectral changes which took place as the comet approached the sun; between August and the end of October a number of “unknow” radiations between λ 4100 and λ 4000 suffered a considerable diminution of intensity as compared with other radiations. The wave-lengths of these lines, considered precise to 1 Á, are 4099, 4074, 4065, 4051, 4041, 4032, and 4016. These radiations where peculiar to the nucleus of the comet, being found neither in the coma nor the tail, and as they became fainter the tail radiations became strong; it was also noted that in the later spectra the tail radiations extended well to the front of the comet's head, showing that in active comets, such as this one and Morehouse's, the tail matter is expelled in all directions. In Kiess's comet it appeared to escape from one point only. Altogether 47 monochromatic images of the nucleus were counted on the Juvisy plates, but the kathode spectrum of nitrogen was not recognised among them.