Notice of an extraordinary luminous appearance seen in the heaven on the 17th of March, 1843, in a letter to S. H. Christie, Esq., Sec. R. S., by Sir John F. W. Herschel, Bart., F. R. S

Abstract

My Dear Sir, —This evening, at half-past seven o’clock, I received notice from one of my servants of a luminous appearance in the sky, visible towards the S. W., which I immediately ran out to ob­serve, and which, as it differed in some remarkable particulars from any phenomenon of the kind I have ever before observed or seen described, I think it not unlikely to prove interesting to the Royal Society. The evening was one of uncommon serenity and beauty: the moon, only thirty-eight hours after the full, having considerable south declination, was not yet risen. In consequence, the sun being already far enough below the horizon to leave only a faint glow of twilight in the west, the stars shone with unsubdued brilliancy, no cloud being visible in any quarter. Orion in particular was seen in all its splendour; and commencing below that constellation, and stretch­ing obliquely westward and downwards, nearly, but not quite to the horizon, was seen the luminous appearance in question. Its general aspect was that of a perfectly straight, narrow band of con­siderably bright white cloud, thirty degrees in length, and about a degree and a quarter, or a degree and a half in breadth in the middle of its length; its brightness nearly uniform, except towards the ends, where it faded gradually, so that to define its exact termination at either end was difficult. However, by the best judgement I could form, it might be considered as terminating, to the eastward or fol­lowing side, at, or a very little beyond, the stars t, k , λ Leporis, which stars (being of the fifth, or at most 5.4 magnitude) were pretty con­spicuously visible; from which circumstance the degree of bright­ness of the ground of the sky in that region may be well estimated. Between these stars and μ Leporis, the luminous band then commenced, involving neither of them, but more nearly contiguous to k and λ than to μ . From thence its course was towards π Eridani, which star must have been covered by it, and was not seen; this judgement of its direction having been formed by noticing that it passed clearly above γ Eridani, and as clearly below and parallel to the direction of δ, ε Eridani, which two stars being dimmed by the vapours of tie horizon and the twilight, were so little conspicuous as perfectly to account for π not having been noticed. At the point of its passage between γ and δ it was still considerably bright, and as it terminated with somewhat more abruptness at a point beyond ε (then about 12° high) than at its upper extremity, I am rather disposed to consider this end as somewhat curtailed by the vapours Making no allowance, however, for this, and estimating its visible termina­tion at a point on a celestial globe nearly opposite ζ Eridani (which star however was not noticed at the time), the length above assigned to the luminous band (30°) has been concluded by measurement on the globe.