The Heights of Auroras

Abstract

THE rare part of the phenomena described by your correspondents is the extreme narrowness of the auroral arches seen on the 10th in the north of Scotland, and on the 11th at Ryde. I take all the other descriptions on the 11th to refer to one arch—a different one from that seen at Ryde; and it was a much wider one, and therefore less unusual, its width having been about 5° as seen here. Your correspondents do not give its width, except that, as seen from Nottingham, it was evidently very broad, and is not stated to have been an arch at all, though I should suppose it was one. The observation at Nottingham Forest, compared with those further north, gives a good opportunity for ascertaining the height of the top of the aurora; but, as Mr. A. Marshall has not given the altitude of the base of the aurora as seen from Nottingham, there are no materials for calculating the height of that. I made several observations of the position of the central line of the arch. I might specify that at 9.25 it was at R.A. 20h. 42m., Decl. + 33½°, and R.A. oh. 43m., Decl. + 33°, and it moved very slowly.