The Aurora Borealis of Feb. 4th

Abstract

ABOUT six o'clock on Sunday evening the ruddy appearance of the upper clouds gave warning of an aurora in prospect, but I was not prepared for the magnificent sight which appeared on looking out an hour later. The higher part of the sky seemed covered with bright rose-coloured clouds, which, from the dark masses of clouds passing underneath, seemed continually to be shifting in position. Intervals of deep green appeared amongst the red, and these, when looked at with a spectroscope, gave a stronger light than their surroundings. Objects near were illuminated as if the moon had risen behind the clouds. I had a miniature spectroscope of Browning's, with which I examined the brightest parts, and obtained four lines—one very bright green, two very faint nebulous green bands, and one red line. Having a spirit lamp handy, in which were remnants of sodium, lithium, and sulphate of copper, I was able roughly to estimate the positions of the lines. The red was about a third from D towards the lithium line; the very bright green about a third from D to the copper line near b, the other faint green bands were more refrangible, and I should think their places were between b and F, and near F, but I could not get their positions so well as the other two; certainly the most refrangible was not so far as the violet-potassium line which I could see in the field.