Doubtless there are excellent reasons for rejecting the theory that a massive body like a planet, or a nebulous mass like those which are found among the star-depths (the least of which would exceed many times in volume a sphere filling the entire space of the orbit of Neptune), fell on some remote sun in the Northern Crown. But there are no sufficient reasons for rejecting or even doubting the theory that a comet, bearing in its train a flight of many millions of meteoric masses, falling directly upon such a sun, might cause it to shine with many times its ordinary lustre, but only for a short time, a few months or weeks, or a few days, or even hours. In the article entitled “Suns in Flames,” in my “Myths and Marvels of Astronomy,” before the startling evidence recently obtained from the star in Cygnus had been thought of, I thus indicated the probable effects of such an event:—“When the earth has passed through the richer portions (not the actual nuclei be it remembered) of meteor systems, the meteors visible from even a single station have been counted by tens of thousands, and it has been computed that millions must have fallen upon the whole earth. These were meteors following in the trains of very small comets. If a very large comet followed by no denser a flight of meteors, but each meteoric mass much larger, fell directly upon the sun, it would not be the outskirts but the nucleus of the meteoric train which would impinge upon him. They would number thousands of millions. The velocity of downfall of each mass would be more than 360 miles per second. And they would continue to pour in upon him for several days in succession, millions falling every hour. It seems not improbable that under this tremendous and long-continued meteoric hail, his whole surface would be caused to glow as intensely as that small part whose brilliancy was so surprising in the observation made by Carrington and Hodgson. In that case our sun, seen from some remote star whence ordinarily he is invisible, would shine out as a new sun for a few days, while all things living, on our earth and whatever other members of the solar system are the abodes of life, would inevitably be destroyed.”
There are, indeed, reasons for believing, not only, as I have already indicated, that the outburst in the sun was caused by the downfall of meteoric masses, but that those masses were following in the train of a known comet, precisely as the November meteors follow in the train of Tempel’s comet (II., 1866). For we know that November meteoric displays have been witnessed for five or six years after the passage of Tempel’s comet, in its thirty-three year orbit, while the August meteoric displays have been witnessed fully one hundred and twenty years after the passage of their comet (II., 1862).[15] Now only sixteen years before the solar outburst witnessed by Carrington and Hodgson, a magnificent comet had passed even closer to the sun than either Tempel’s comet or the second comet of 1862 approached the earth’s orbit. That was the famous comet of the year 1843. Many of us remember that wonderful object. I was but a child myself when it appeared, but I can well remember its amazing tail, which in March, 1843, stretched half-way across the sky.
“Of all the comets on record,” says Sir J. Herschel, “that approached nearest the sun; indeed, it was at first supposed that it had actually grazed the sun’s surface, but it proved to have just missed by an interval of not more than 80,000 miles—about a third of the distance of the moon from the earth, which (in such a matter) is a very close shave indeed to get clear off.”
We can well believe that the two meteors which produced the remarkable outburst of 1859 may have been stragglers from the main body following after that glorious comet. I do not insist upon the connection. In fact, I rather incline to the belief that the disturbance in 1859, occurring as it did about the time of maximum sun-spot frequency, was caused by meteors following in the train of some as yet undiscovered comet, circuiting the sun in about eleven years, the spots themselves being, I believe, due in the main to meteoric downfalls. There is greater reason for believing that the great sun-spot which appeared in June, 1843, was caused by the comet which three months before had grazed the sun’s surface. As Professor Kirkwood, of Bloomington, Indiana, justly remarks, had this comet approached a little nearer, the resistance of the solar atmosphere would probably have brought the comet’s entire mass to the solar surface. Even at its actual distance, it must have produced considerable atmospheric disturbance. But the recent discovery that a number of comets are associated with meteoric matter travelling in nearly the same orbits, suggests the inquiry whether an enormous meteorite following in the comet’s train, and having a somewhat less perihelion distance, may not have been precipitated upon the sun, thus producing the great disturbance observed so shortly after the comet’s perihelion passage.
Let us consider now the evidence obtained from the star in Cygnus, noting especially in what points it resembles, and in what points it differs from, the evidence afforded by the star in the Crown.
The new star was first seen by Professor Schmidt at a quarter to six on the evening of November 24. It was then shining as a star of the third magnitude, in the constellation of the Swan, not very far from the famous but faint star 61 Cygni—which first of all the stars in the northern heavens had its distance determined by astronomers. The three previous nights had unfortunately been dark; but Schmidt is certain that on November 20 the star was not visible. At midnight, November 24, its light was very yellow, and it was somewhat brighter than the well-known star Eta Pegasi, which marks the forearm of the Flying Horse. Schmidt sent news of the discovery to Leverrier, at Paris; but neither he nor Leverrier telegraphed the news, as they should have done, to Greenwich, Berlin, or the United States. Many precious opportunities for observing the spectrum of the new-comer at the time of its greatest brilliancy were thus lost.
The observers at Paris did their best to observe the spectrum of the star and the all-important changes in the spectrum. But they had unfavourable weather. It was not till December 2 that the star was observed at Paris, by which time the colour, which had been very yellow on November 24, had become “greenish, almost blue.” The star had also then sunk from the third to far below the fourth magnitude. It is seldom that science has to regret a more important loss of opportunity than this. What we want specially to know is the nature of the spectrum given by this star when its light was yellow; and this we can now never know. Nor are the outbursts of new stars so common that we may quickly expect another similar opportunity, even if any number of other new stars should present the same series of phenomena as the star in Cygnus.
On December 2, the spectrum, as observed by M. Cornu, consisted almost entirely of bright lines. On December 5, he determined the position of these lines, though clouds still greatly interfered with his labours. He found three bright lines of hydrogen, the strong double sodium line in the orange-yellow, the triple magnesium line in the yellow-green, and two other lines—one of which seemed to agree exactly in position with a bright line belonging to the solar corona. All these lines were shining upon the rainbow-tinted background of the spectrum, which was relatively faint. He drew the conclusion that in chemical constitution the atmosphere of the new star was constituted exactly like the solar sierra.
Herr Vögel’s observations commenced on December 5, and were continued at intervals until March 10, when the star had sunk to below the eighth magnitude.
Vögel’s earlier observations agreed well with Cornu’s. He remarks, however, that Cornu’s opinion as to the exact resemblance of the chemical constitution of the star’s atmosphere with that of the sierra is not just, for both Cornu and himself noticed one line which did not correspond with any line belonging to the solar sierra; and this line eventually became the brightest line of the whole spectrum. Comparing his own observations with those of Cornu, Vögel points out that they agree perfectly with regard to the presence of the three hydrogen lines, and that of the brightest line of the air spectrum (belonging to nitrogen),—which is the principal line of the spectrum of nebulæ. This is the line which has no analogue in the spectrum of the sierra.