Popular Science Monthly/Volume 21/June 1882/Astronomical Panics
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By Daniel Kirkwood
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By DANIEL KIRKWOOD.
WHEREVER science has not been cultivated, all new and startling appearances in the sky are regarded as supernatural. But a few years since a shower of meteoric stones fell in India, the fall being attended by terrific explosions. The alarmed inhabitants of the district believed these masses of rock to have been thrown by their deities from the Himalaya Mountains, and with great veneration gathered up the fragments to be kept as objects of religious worship. Nor need we smile at this example of recent superstition. In the most civilized countries of the ancient world such phenomena as the aurora borealis, total eclipses, comets, and meteoric showers, were viewed as miraculous displays of divine power, and generally as forerunners of impending disasters. A brief account of some of the panics thus produced may not be without interest.
No one who has seen the more brilliant displays of the northern lights the splendid coronal arch, the columns tinged with various colors and moving in silent grandeur upon the midnight sky can wonder that in a superstitious age their appearance should have excited the utmost consternation. Before the eighteenth century no physical explanation of such displays had been suggested or even thought of. The phenomena appeared suddenly and unexpectedly, and could not be referred to natural causes then known. The excited imagination saw armies mustering in the sky, brandishing their spears and raising aloft in quick succession their bloody lances. A very brilliant aurora seen in England, in 1575, is described by a writer of that period as a chasm formed in the northern sky, in which "were seen a great many bright arches, out of which gradually issued spears, cities with towers, and men in battle array; after that there were excursions of rays in every direction, waves of clouds, and battles in which some were fleeing, some pursuing, and others wheeling around in a surprising manner." If panics of this nature have ceased, the fact is due to the ever-advancing light of physical science.
One of the most noted eclipses in history is that recorded by Herodotus, and which occurred in the year 585 b. c. The panic produced by this eclipse put an end to the war between the Medes and the Lydians. A great battle was in progress, when, suddenly, day was turned into night by a total eclipse. The contending armies, struck with consternation, at once laid down their arms and hastened on both sides to conclude a peace.
The Eclipse of Laeissa. Xenophon, in his "Anabasis," Book III, chapter iv, relates how the excitement and alarm produced by a total eclipse led to the surrender of a city. When the Persians obtained the empire from the Medes, their king besieged the ancient city of Larissa, but failed to capture it till, finally, the inhabitants, terror-stricken by the darkness of a solar eclipse, lost all courage, and so the city was taken.
A total eclipse of the sun was visible at many places in Europe on May 12, 1706. Professor Grant relates, in his "History of Physical Astronomy," that in many parts of the city of Geneva persons were seen during the totality "prostrate on the ground and offering up prayers, under the impression that the last day was come."
An ancient writer, in describing the great meteoric shower of the year 1202, says: "The stars flew against one another like a scattering swarm of locusts, to the right and left; this phenomenon lasted until daybreak; people were thrown into consternation and cried to God, the Most High, with confused clamor." Similar consternation and alarm were exhibited during the great meteoric display of 1366. An historian of that time says, "Those who saw it were filled with such great fear and dismay that they were astounded, imagining that they were all dead men, and that the end of the world had come."
The terror an# alarm produced among the colored people of the South by the great star-shower of 1833 have been so often described that the details need not here be repeated. I may, however, remark in passing that this shower was derived from the same meteoric swarm that produced the displays of 1202 and 1366, to which I have referred, and which returns at intervals of thirty-three years and three months.
In former ages comets were regarded as signs sent directly by the Diety to announce coming wars or fatal disasters. The degree of terror which they excited was proportioned to the size of the comet or the form and length of its train. A great comet, believed to have been that of Halley, appeared in April, a. d. 1066, the year in which William the Conqueror invaded England. This comet was looked upon as the forerunner of the conquest, and produced universal alarm. "The new star means a new king," was the common expression of the day. All writers of that period bear witness to the splendor of the comet of 1066.
But the accounts of all great comets in ancient times furnish similar instances of superstitious dread and consternation. Of a different nature was the alarm produced among the ill-informed in 1832 by the baseless expectation of the earth's collision with Biela's comet. It had been announced by astronomers that on a particular day a part of the earth's orbit would be included within the nebulosity of the comet. This statement was misunderstood by the general public, and a coming together of the earth and the comet was by many apprehended. Astronomers well knew, however, that our planet would be millions of miles from the intersection of the two orbits before that point could be reached by the comet.
The latest instance of supposed danger from a comet is that founded on a misapprehension of an article by the distinguished Mr. Proctor. In 1668 a large comet appeared and passed very near to the sun's surface probably through the upper strata of its atmosphere. The great comet of 1843 moved so nearly in the same path that it was supposed by some astronomers to be a return of the same body; the period being one hundred and seventy-five years. But the path of the bright comet seen in the southern hemisphere in 1880 coincided still more nearly with that of the comet of 1843, and these dates would indicate a period of only thirty-seven years. Either, therefore, the period is becoming rapidly shorter, or the comets are separate bodies moving in orbits which, within the limits of the planetary system, are nearly co-incident. The latter alternative has, I think, the greater probability. The theory, however, that the comets of 1668, 1843, and 1880 were returns of the same body, and that its orbit is converging with great rapidity, has been defended as affording a plausible explanation of the similarity of elements. At a meeting of the Royal Astronomical Society of London, May 14, 1880, Mr. Marth, a well-known astronomer, remarked as follows:
"Supposing this comet of 1843 is the same as that of 1668, it would not be very wonderful that it should reappear now after thirty-seven years, instead of one hundred and seventy-five years. The velocity of a body moving in the solar system depends simply on its distance from the sun, and on the major axis of its orbit. If the velocity is reduced by a resisting medium, there will be a reduction of the major axis, and there is nothing whatever unreasonable in the supposition that, however weak the corona may be, its resistance would have a very great effect upon the motion of a comet which rushes through it, so that I should not be at all surprised if it should turn out that this comet of 1880 is the same as the comet of 1843 and that of 1668, and that its revolution has been so much affected that possibly it may return in, say, seventeen years."
These remarks of Mr. Marth were some time since quoted by Mr. Proctor, and made the basis of an article which in unscientific circles produced to some extent a most absurd sensation. Mr. Proctor's remarks on the subject have been misinterpreted as indicating the probable destruction of life upon the earth about the close of the present century. His language, however, though somewhat unguarded, expressed no such opinion.
The three comets named above approached nearer the sun than any other known, except, perhaps, that of 1680. In fact, when nearest the sun they actually grazed the solar atmosphere, or passed through its outermost portions. Now, it is well known that the motion of a planet or comet through a resisting medium continually lessens its distance, and hence accelerates its velocity. Messrs. Marth and Proctor assume that the passage of the comet of 1668 through the outer portions of the sun's atmosphere reduced its previously long but unknown period to one hundred and seventy-five years, so that its next appearance was in 1843. The perihelion distance at that date was still less; the comet met with greater resistance, and the period was shortened to thirty-seven years. The time of revolution would thus be lessened at each successive return, and ultimately the comet would plunge into the sun. Striking the solar surface with a velocity of three hundred and fifty miles a second, the amount of heat produced by the concussion and radiated to the earth might raise the temperature to such a degree as to destroy life upon our planet. Such are the conjectures suggested in Mr. Proctor's paper. Let us briefly consider them.
In the first place, the fact on which the theory of the supposed catastrophe is based viz., the identity of the three comets is extremely doubtful. It is much more probable, in view of all the circumstances, that they are different bodies moving in similar orbits.
Again, the period of seventeen years, fixing the comet's next return, according to Mr. Marth, about 1897, was the merest conjecture, not founded on any mathematical calculation whatever. It is true that the passage o a comet through the sun's atmosphere would shorten its period at each return. The absorption of the comets of 1843 and 1850 by the sun's gaseous envelope, at some time in the distant future, is therefore by no means improbable. Such results are not known to have occurred in historic times; but, if the sun is gradually contracting i n other words, if its diameter was once considerably greater than at present any comet passing so near the center as that of 1880 would have plunged so deeply into the sun's atmosphere as to be absorbed into its mass. It is true, moreover, that, when the motion of a body is arrested, such motion is converted into heat. If the earth were stopped in its orbit, its fall upon the sun would produce an amount of heat equal to that now radiated in ninety years. If the mass of the comet being that of the earth, the heat produced by the impact would scarcely be equal to that now radiated in seven days; or, if the cometary mass be only equal to that of a globe one hundred miles in diameter, and of the same density as the earth, the additional amount of heat would be less than that now supplied in a single hour. It may further be remarked that the collision would be as likely to occur on the hemisphere turned away from the earth as on that turned toward us.
But let us assume that the great southern comet of 1880 was in fact a return of the comet of 1843, that its present period is about thirty-seven years, and that in consequence of its passage through the outer-most strata of the sun's atmosphere its period must be shortened more and more until it falls upon the sun's surface. The solar atmosphere is known to be very rare from the fact that matter thrown out by the sun's eruptive force has been seen to ascend to a height of two hundred thousand miles. The resistance which it would offer to the comet's motion would therefore be slight, and in all probability several centuries would elapse before the comet's course would be terminated by its falling upon the sun. Instead, therefore, of a sudden catastrophe, we should have a gradual dissolution of the comet; portions becoming absorbed by, or incorporated with, the solar atmosphere at each successive perihelion passage. The apprehension of danger to the earth from a great and sudden increase of the sun's heat is, therefore, without any reasonable foundation.
It is due to Mr. Proctor to say that he did not designate the year 1 897, nor indeed any other, as that in which the comet would fall into the sun, nor did he express the opinion that the collision would occur at the cornet's next return. He merely remarks that, "if already the comet experiences such resistance in passing through the corona when at its nearest to the sun that its period undergoes a marked diminution, the effect must of necessity be increased at each return, and after only a few, possibly one or two, circuits, the comet will be absorbed by the sun." This statement, though perhaps incautiously expressed, is very different from that attributed by unscientific readers to its distinguished author.