Our Astronomical Column

Abstract

HELIUM ABSORPTION IN THE SOLAR SPECTRUM.—In a letter to the Observatory (No. 386, p. 315./August) Mr. Nagaraja, of the Kodaikanal Observatory, records the results of some further observations of the helium line, D3, as a dark line in thel spectrum of the sun. Having already frequently observed this dark line in the regions of the photosophere adjacent to sun-spots, he suspected that he had also seen it as a faint line in the ordinary solar spectnum. but for several reasons found the observation difficult to confirm. He now states that, with a recently mounted large grating spectrograph, he obtained a photograph of the D3 region on April 19, and on examination found that it shows both the darkening and the chromospheric (bright) line, where a spot was close to the limb, and, further, both the dark and the bright lines appear to be a continuation of a faint line in the normal solar spectrum. Further examination is necessary are the identity of this faint line with the helium line can be definitely affirmed, and to this end Mr. Nagaraja proposes to carry on the research.