Tuesday, January 24, 2017

Donati's Comet 1858

I stumbled across the article below while researching for "Historical Fiction Writer's Guide to Carriages & Wagons of the 19th Century." The article that was published in the Nov. 1858 issue of the New York Coach-Maker's Magazine.

Donati's comet, which at this date so beautifully adorns the western sky from dusk until half-past eight in the evening, and again is seen in the northeast at about four in the morning, was nearest the earth about the 9th of October, at which time it was very large and brilliant, probably more so than any that may be seen again by the present generation. Its distance, when nearest the earth, was about fiftytwo millions of miles. The nucleus was near the constellation Arcturus, and nearest the earth's orbit on the 20th of October. Dr. Bond, of Harvard College Observatory, says that the cause of this comet's appearance again in the morning is owing to the considerable northern declination of the comet, with a right ascension differing but little from that of the sun.
The following very interesting observations on the progress of the comet, at an early date after its appearance, are from the pen of Professor Mitchell, of the Cincinnati Observatory, and will, no doubt, be read with interest at this time:
"On the evening of the 25th of September, the appearance of the comet, in the great refractor of the Cincinnati Observatory, was especially interesting. The central portion, or nucleus, was examined with powers varying from one hundred to five hundred, without presenting any evidence of a well-defined planetary disc. It was a brilliant glow of light, darting and flashing forward in the direction of the motion toward the sun, and leaving the region behind in comparative obscurity. But the most wonderful physical feature presented, was a portion of a nearly circular nebulous ring, with its vertex directed toward the sun, the bright nucleus being in the centre, while the imperfect ring swept more than half round the luminous centre. This nebulous ring resembled those which sometimes escape from a steam-pipe, but did not exhibit the appearance which ought to be presented by a hollow hemispherical envelope of nebulous matter.

"There was an evident concentration of light in the central portions of the ring, while, in the case of a hollow envelope, the brightest portion should be at the outer edge. By micrometrical measurement, the distance from the central point to the circumference of the ring was found to be about nine thousand miles. This would give a diameter of eighteen thousand miles, in case the ring was entire. Similar measurements, made on the evening of the 26th of September, indicated a decided increase in the radius of the ring, which was now not less than twelve thousand miles in length. On the same evening, I noticed the fact that the luminous envelope did not blend itself into the head portion of the tail, but appeared somewhat to penetrate into this nebulous mass, especially on the upper part, presenting the appearance of about 200 degrees of a spiral. The tail, on the 25th, was decidedly brighter and better defined on the upper than on the lower portion, while on the evening of the 26th there was a much nearer approach to equality in brightness, especially near the head of the comet. Through the telescope, and near the head, the tail presented the appearance of a hollow nebulous envelope, under the form of a paraboloid of revolution, the edges being brightest and well defined, while there was a manifest fading away of light towards the central region. Through the vast depth of nebulous matter composing this wonderful appendage, the faintest telescopic stars shone with undiminished brightness.
"The only comet which has presented an appearance resembling the one now visible is the one known as Halley's Comet, as seen by Sir William Herschel and others, in its return in 1836. There is a marked difference between the two: that while the envelope of Halley's Comet is described as a hemispherical hollow envelope, this shows more the shape of a nebulous ring; there is a faint, misty light, of irregular outline, but not to be mistaken by even a casual observer. Mr. J. R. Hind, the English astronomer, who has earned the appellation of the 'Planet-catcher,' is good authority on the comet. He expresses the opinion that its increase in brightness will go on, in conformity with theory, so that about the epact of maximum brilliancy in October it will be visible with telescopes in full sunshine. The nucleus is of the appearance of a star of the second magnitude, and the tail, which points nearly due North, although rather faint, is about five degrees in length. The comet is about 120 millions of miles from the earth, or a little farther from us than the sun, and the diameter of the nucleus is estimated to be rather more than 3,000 miles, or nearly one and a half times larger than the moon. The length of the tail, judging from its appearance, is estimated at fifteen millions of miles. The path of the comet is that of a parabola, and it is conjectured that it will not appear again for some hundreds of years."

We have had our engraving made expressly for this Magazine, and which gives a very fair representation of it as it appeared on the evening the drawing was made.

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