M. Bernard Lyot

Abstract

THE Gold Medal of the Royal Astronomical Society has been awarded to M. Bernard Lyot, of the Meudon Observatory, France, for his observations and photography of the solar corona in the absence of a total eclipse. In 1868, Lockyer and Janssen showed that prominences could be observed when the sun was not eclipsed. In 1882, Huggins attempted the more difficult problem of observing the corona without an eclipse, and both Hale and Deslandres in 1893 designed apparatus for the chromatic isolation of the green line. These efforts were entirely unsuccessful. M. Lyot went much more thoroughly into the optical conditions necessary to eliminate the diffused sunlight. The light of the sun is a million times that of the corona, and at Meudon the scattered sunlight at I′ from the sun's limb cannot be reduced to less than twenty or thirty times that of the corona, but on the Pic du Midi, after a fall of snow, the stray light on occasions is not of greater intensity than the light of the corona at l′ from the limb. But a very large amount of stray light is incidental in the optical systems usually employed, which M. Lyot has analysed, into diffraction round the edge of the objective lens, scratches and bubbles on the lens, and reflected light from the back of the lens. By arranging screens to cut off the light from these several sources, he has succeeded in photographing the inner corona, obtaining a spectroheliogram in light 5303 A., and measuring the polarization all around the limb; in addition, he has obtained accurate wave-lengths of a number of the emission lines of the corona, as well as the width of the lines.