Can Aurora be Seen in Daylight?

Abstract

I VENTURE to believe not, in spite of circumstantial accounts to the contrary, and I ground my belief on the following considerations:—I. No description of a daylight aurora that I have ever seen will bear a critical examination. Take that published in the last number of NATURE. Here two arcs of faint white lines are said to have been seen in a direction “almost due east,” and certainly the illustration given is not very unlike the appearance that auroral arcs sometimes present. But auroral arcs, so far as I know, never appear in the east, and the conclusion, therefore, is unavoidable that the object observed was nothing more than a remarkably symmetrical form of cirrus cloud. In another instance, lately published, although the thing described is called a daylight aurora, I fail to see in the description anything more than an account of the appearances presented when a high canopy of cloud clears off bodily from the sky with a sharp, straight edge, which by perspective becomes an arch. In the case referred to, the clouds clearing off from the direction of magnetic north, the arch corresponded in position with that of an aurora, and hence was set down as auroral. In a third account of a daylight aurora, it is expressly mentioned that the sky was hazy, and a solar halo visible, a condition of things which, while it would make the occurrence of aurora-like cirrus extremely probable, would be specially unfavourable to the visibility of a true aurora; for certainly if so delicate and phosphorescent a light as that of an aurora is to be seen at all in the daytime, it can only be under circumstances the most favourable as regards clearness of the lower atmosphere.