“Halo”: Pink Rainbow

Abstract

THE appearance noted in NATURE this week (p. 268) by Prof. O'Reilly must surely have been a case of the rayons du crépuscule that are frequently visible near sundown in the eastern sky. East-south-east cannot at this season be very far from opposite the setting sun. Prof. O'Reilly does not mention, though probably it was the case, that the point of convergence of the “beams” which he saw was diametrically opposite the sun's position. That these beams appeared dark is probably merely caused by the real “rayons” being wide, with narrow, darker interspaces between. I have several times (see Phil. Mag., 1877) called attention to the existence of similar rays crossing the rainbow radially; indeed, it is seldom that a rainbow occurs when the sun is low in the sky, without one or more such rays being visible within the are. Two such rays, for example, were visible in a bow seen here at sunset two evenings ago. This bow was interesting in another way also; for, like the “pink” rainbows about which there was some correspondence in NATURE last year, the only colours visible (in the primary are) were red and yellow, the red being of a pinkish rather than a crimson hue.