Zodiacal Light

Abstract

THE evening of Feb. 2 being clear, after a long persistence of rainy cloud for many days, about 6.5 P.M. I began to notice the existence of a zodiacal light. Some time later, probably about 6.40, it was considerably brighter than any portion of the galaxy in sight at the time, though this might not have been the impression of an inattentive spectator, as the gradual melting away of its edges produced much less contrast with the ground of the sky than the better denned outline of the Milky Way. Its light was, in fact, so imperceptibly diffused that it was impossible to fix its boundaries or extent with any accuracy. Its general position was, however, undoubtedly a Utile below the square of Pegasus (where its upper edge fell short of α and γ), and beneath the three stars of Aries; but its light was here so enfeebled that its termination was quite uncertain, and it could only be said that the direction of its axis was towards the Pleiades. Its breadth where most brilliant, near Pegasus, might probably be estimated at 8° or 9°, from comparison with the distance from α to β, and with the length of the belt of Orion; but this determination was liable to great uncertainty. It was thought to show a ruddy tinge, not unlike the commencement of a crimson Aurora Borealis; this may have been a deception, but it was certainly redder or yellower than the galaxy. At 7 I examined it with a little pocket spectroscope, which shows very distinctly the greenish band of the aurora; but nothing of the kind was visible, nor could anything be traced beyond a slight increase of general light, which, in closing the slit, was extinguished long before the auroral band would have become imperceptible. It was still visible at 8.30. The phenomenon had been previously noticed, but with less distinctness, on Dec. 30 and Jan. 11.