Popular Science Monthly/Volume 23/June 1883/Recent Magnetic Storms and Sun-Spots
|RECENT MAGNETIC STORMS AND SUN-SPOTS.|
NO one who beheld the great auroral displays of last year can ever forget the impression that they made. They were among the most glorious celestial spectacles that have been witnessed in our latitudes. The first one occurred on the night of Sunday, April 16th. On the afternoon of that day I was watching with a telescope two complicated sun-spots, or groups of spots, one of enormous size, which had made their appearance on the solar disk several days before. My attention had been particularly attracted to these spots, both on account of their great size and because I thought I could perceive changes going on in them under my eyes. After watching them through the afternoon I became satisfied, about an hour before sun-down, that the smaller spot, which was considerably in advance of the other, and was rapidly approaching the sun's meridian, had visibly increased in size while I had been watching it, and that perceptible changes had taken place in the complicated cluster of nuclei constituting the black center of the greater spot. It was evident that a tremendous outburst of solar forces was occurring; but, although I knew of the well-established connection between such convulsions in the sun and the condition of the earth's magnetic elements, I was not prepared for the spectacle that followed.
The sun had been below the horizon only long enough for the lengthening spring twilight to fade from view, when a pale-green arch of light was seen spanning a broad arc of the northern horizon, while above it the mysterious streamers and curtains of the aurora were waving and coruscating in the sky. So quickly had the earth responded to the magnetic impulse from the storm on the sun. The popular excitement caused by this aurora was remarkable, especially among those who were not aware of the nature of the strange illumination in the sky. People gathered in knots at the street-corners, and in the little parks of the city, and gazed wonderingly at the flaming heavens. Many seemed to be seized with a mingled feeling of admiration and dread. I crossed the Fulton Ferry after midnight, when the auroral streamers were yet shooting from horizon to zenith, and Arcturus was shining brilliantly in the center of a complete crown of greenish-yellow light near the zenith. A throng gathered at the bow of the boat to watch the display, which was much more brilliant when seen from the center of the stream, away from the glare of the streetlamps. A decently-dressed and not unintelligent-looking man asked me, with a troubled look, and pointing to the heavens:
"What is that?"
"It's the aurora borealis," I replied.
He seemed relieved to find some one who could give it a name, and who did not appear to be alarmed.
"I thought it might be the comet the papers are talking about," he said, "and I didn't know what was going to happen."
I know that this man's vague fears were shared by others.
Everybody who had anything to do with telegraphs will remember the effects of the aurora. The wires played strange freaks. In some places they were disconnected from the batteries and worked by means of the current furnished by the magnetic storm; in other places they refused to work at all. The Atlantic cable was crippled, and at intervals, for several days thereafter, there was considerable delay of all telegraphic business. Subsequently it was learned that the auroral storm had raged, simultaneously, not only in the United States and Canada, but in Great Britain, on the Continent of Europe, and in Asia, extending clear across to the shores of China.
The next day, when I turned my telescope upon the sun, I was astonished at the changes that had taken place. The smaller spot, which I had seen increasing in magnitude on the previous day, had swollen to between five and six times its former size, so that now it was about half as large as the larger spot, and both were clearly visible to the unassisted eye, shaded with a dark glass.
I find by reference to the exact measurements of these spots, made at the Greenwich Observatory, that, whereas on the 16th the area of the smaller spot was to that of the larger about as 1 to 13·6, on the 17th the relative magnitudes were about as 1 to 2·2.
For three or four days afterward there were magnetic disturbances and occasional auroral displays at night, and during this time the activity of the solar forces continued.
On the 19th there was another magnetic storm, and coincidently with it the smaller spot suddenly increased in size again, until it was nearly as large as the other, and on the 21st it actually surpassed its neighbor in magnitude. After that both groups rapidly waned, the one which had undergone the remarkable development I have described fading much faster than the other one.
The next great display of sun-spots accompanied by auroras and magnetic disturbances—if we except one or two of minor importance and a somewhat remarkable one seen in Europe, which will be described hereafter—occurred in November last, culminating on the 17th of that month in one of the greatest magnetic storms on record, which crippled the telegraphs almost all over the civilized world. In Europe fine auroras were observed on the 12th, 13th, 14th, 15th, 16th, 17th, and 19th, accompanied by more or less magnetic disturbance. During that time a tremendous sun-spot, exceeding in size the largest of the April spots, was advancing from the edge of the disk to the center. In this country the principal auroral displays were on the nights of the 17th and 19th, and the chief force of the magnetic storm was felt on the 17th. On that day a storm of rain and snow prevailed over most of the Union, and simultaneously with this storm there raged a hurricane of magnetic forces. The effects were similar to those witnessed during the April storm, but more intense. As in April, some wires were worked without batteries, while others could not be worked at all. Cable communication was interrupted. Some startling phenomena occurred. Sparks of fire leaped from the wires and instruments. In the West, switch-boards were burned and Fig. 1. keys melted. Operators received severe shocks. Practical telegraph men said they had never known such a powerful disturbance of the magnetic elements. In the evening, when the sky cleared at Chicago, a most magnificent sight was beheld in the heavens. The brilliancy of the aurora far exceeded that of the April display. A singular feature of this aurora, which was also noticed in Europe, was a splendid luminous arch spanning the sky from east to west and passing nearly through the zenith. Another feature that added brilliancy to the spectacle was the variety of color visible. The prevailing tints were rose-color and green, but in some places streamers and patches of violet, yellow, and orange light were seen. On the night of the 19th and morning of the 20th, the sky having cleared here, a splendid aurora was seen in New York. The magnetic disturbance also continued.
At the April meeting of the American Astronomical Society I exhibited some magic-lantern views representing the principal changes which took place in the great sun-spot during the magnetic storm of November. These views, copied from drawings of the spot made at the telescope, are reproduced in the accompanying cuts.
Fig. 1 represents the spot as it appeared on the 16th of November, the day before the culminating magnetic disturbance took place. Low magnifying powers, varying from sixty-five to a hundred and ten diameters, were used while making the drawings, as it was not desired to obtain pictures representing all the details. Consequently, only the principal features of the spot are here represented, but the reader will be able to get a better general idea of the changes that occurred from such a picture than he could from one filled with minor details. The central and lower portions of the figure are especially worthy of attention because of the indications they give of an eddying motion corresponding with what should always be seen in a sun-spot according to Faye's cyclonic theory, but which, in fact, is rarely visible. It was also in these parts of the spot that the principal changes occurred, as will be seen by reference to the figures. It is very interesting to note that in Carrington's drawings of the remarkable sun-spot which accompanied the great magnetic storm of September, 1859—a disturbance whose effects strikingly resembled those produced by the storm of last November—similar indications of a whirling motion can be detected. Another exceedingly interesting fact is that in England, on the 16th of November last, luminous points were seen rapidly crossing the great spot. This forcibly recalls the similar phenomenon of flying points of light, seen by Carrington and Hodgson, darting across the spot of 1859, and which seemed to be a signal for the outbreak of the magnetic storm that followed.
In Fig. 2, which represents the spot as it appeared on the 18th, the day after the great magnetic storm, evidences of cyclonic motion are still, perhaps, visible, though they are rather suggested by a comparison of the appearance of the spot with that shown in the previous figure than by any clear indications in the figure itself unconnected with the other one. The roundish, nuclear mass near the center suggests by its form a whirlpool-like motion, but it is difficult on that hypothesis to account for the long, straight channel connecting it with the oblong figure on the right. The peculiar crooked figure seen in the lower part of the first picture has, it will be perceived, apparently broken up into several fragments, but this by itself is not inconsistent with the theory of an eddying motion.
Fig. 3 represents the appearance of the spot on November 19th, auroras and magnetic disturbances having in the mean time continued. Still further changes, it will be seen, have taken place, and the lower portion of the spot shows a tendency to separate from the larger mass above—a phenomenon that is of not unfrequent occurrence.
I find, by reference to my note-book, that other changes were visible on the 20th, but unfortunately I was prevented from sketching them. After that, unfavorable weather, and other interruptions, prevented me from sketching the spot, but the sketches that were made cover the period during which the most remarkable changes occurred, as well as that of the greatest magnetic disturbances. In order to
obtain a clear notion of the tremendous forces involved in the changes represented in the drawings, it is necessary to consider the enormous size of the spot as measured in square miles. Counting the whole area covered by the various nuclei and the penumbral depression surrounding them, the spot was not less than 60,000 miles long and 40,000 miles wide. In other words, it covered 2,400,000,000 square miles of the solar surface. The area of the whole surface of the earth, land and sea, is less than 200,000,000 square miles, so that if the crust of the earth had been peeled off like the skin of an orange, spread out flat and plastered against the sun, it would have looked like a mere outlying patch beside the great congeries of sun-chasms constituting this gigantic spot. Masses of gaseous matter, many times greater than the earth in volume, must have been hurled and whirled about there with tremendous velocity in order to produce the changes which the telescope revealed. Milton's description of the battling elements of chaos, through which Satan fought his way, will apply, though inadequately, to the scenes of chaotic fury of which such a sun-spot is the theatre.
In Fig. 4 is represented a very remarkable spot which, because it made its appearance at about the time the great comet was in perihelion, in September last, and broke out on the portion of the solar globe which was nearest to the comet at that time, has been fancifully called the "black eye that the comet gave the sun." There were other spots visible at the same time and they also were ascribed by some to the Fig. 4. influence of the comet. Some plausible reasons have been shown in favor of this view, and Professor Kirkwood's opinion that the great sun-spots of June, 1843, were caused by the large comet of that year has been freely quoted in support of it. Of course, the question whether this particular spot and its companions originated in some disturbance caused by the comet, whether by the fall of meteoric masses following in the comet's track or otherwise, can not be settled either way by positive evidence at present. But, while there are improbabilities in the way of the hypothesis, it may, at least, be said that, if any comet could produce a sun-spot without actually tumbling into the sun itself, the comet of last year ought to have been able to do it, for, as is known, it almost brushed the sun in its perihelion swing.
This great spot, however, is interesting on another account. The cut represents its appearance on October 1st, when it had reached about its greatest development. On October 2d there was a magnetic storm which was felt principally in Europe. The storm was very much less severe in its effects upon the telegraphs than those of April and November, but it was accompanied by the appearance throughout England, Scotland, and Western Europe of a most beautiful aurora.
In conclusion, it may be said that, while the evidence furnished by the great magnetic storms of last year was hardly needed to complete the chain of proof of the intimate connection between solar outbursts and the magnetic conditions prevailing upon our globe, yet this evidence was of such a striking character that it must rank among the most interesting of all that bears upon this question. It is, perhaps, worthy of remark that the period of sun-spot maximum through which we have just been passing has also furnished a good deal of evidence in favor of the views of those who think a connection can be traced between sun-spots and the weather. It is only necessary to point to the facts that 1881 and 1882, as well as the beginning of 1883, have been remarkable for cyclones, tornadoes, storms, and floods, and that, coincidently with these meteorological disturbances, huge spots and other evidences of commotion have appeared in the sun. Here is a splendid field for investigation.