Comets and Meteors Part 7

21. 1800, " 10th.

As the earth is about five days in crossing the ring, its breadth in some parts cannot be less than 8,000,000 miles.

In 1866 Professor Schiaparelli, on computing the orbit of this meteoric stream, noticed the remarkable agreement of its elements with those of Swift's or Tuttle's comet[25] (1862, III.), as computed by Dr. Oppolzer.

These coincidences are exhibited in the following table:

Meteors of Comet III.

August 10. of 1862.

Longitude of perihelion 343 38' 344 41'

Ascending node 138 16' 137 27'

Inclination 63 3' 66 25'

Perihelion distance 0.9643 0.9626.

Period 105 years (?) 121.5 years.

Motion Retrograde. Retrograde.

[25] Mr. Swift, of Marathon, N. Y., had two or three days priority in the discovery of this comet, but unfortunately delayed his announcement of the fact.

It appears, therefore, that the third comet of 1862 is a part of the meteoric stream whose orbit is crossed by the earth on the 10th of August.

The characteristics of different meteor-zones afford interesting indications in regard to their relative age, the magnitude and composition of their corpuscles, etc. Thus, if we compare the streams of August 10 and November 14, we shall find that the former probably entered our system at a comparatively remote epoch. We have seen that at each return to perihelion the meteoric cl.u.s.ter is extended over a greater arc of its...o...b..t. Now, Tuttle's comet and the August meteors undoubtedly const.i.tuted a single group previous to their entering the solar domain. It is evident, however, from the annual return of the shower during the last 90 years, that the ring is at present nearly if not quite continuous. That the meteoric ma.s.s had completed many revolutions before the ninth century of our era is manifest from the frequent showers observed between the years 811 and 841. At the same time, the long interval of 83 years between the last observed display in the ninth century, and the first in the tenth, seems to indicate the existence of a wide chasm in the ring no more than a thousand years since.

Neither the period of the meteors nor that of the comet can yet be regarded as accurately ascertained. The latter, however, in all probability, exceeds the former by several years. Now, at each pa.s.sage of the earth through the elliptic stream, those meteoroids nearest the disturbing body must be thrown into orbits differing more or less from that of the primitive group. In like manner the near approach of the _comet_ to the earth at an ancient epoch may account for the lengthening of its periodic time.

The Meteors of November 27.

Professor Schiaparelli's brilliant discovery of the relation between comets and meteors may now be ranked with the established truths of astronomy. His hypothesis, however, in regard to the _origin_ of meteoric streams has not been generally accepted. Comets and meteors, according to his theory, are derived from cosmical clouds existing in great numbers in stellar s.p.a.ce. These nebulae, in consequence of their own motion or that of the sun, are drawn towards the centre of our system. By the unequal influence of the sun's attraction on different parts, such clouds are transformed into currents of great length before reaching the limits of the planetary system. Shooting-stars, fire-b.a.l.l.s, aerolites, and comets being all of the same nature, differing merely in size, sometimes fall towards the sun as parts of the same current.

The views of Dr. Weiss, of Vienna, differ from those of Schiaparelli, in that he regards comets as the original bodies by whose disintegration meteor-streams are gradually formed.[26] "Cosmical clouds," he remarks, "undoubtedly appear in the universe, but only of such density that in most cases they possess sufficient coherence to withstand the destructive operation of the sun's attraction, not only up to the boundaries of our solar system, but even within it. Such cosmical clouds will always appear to us as comets when they pa.s.s near enough to the earth to become visible. Approaching the sun, the comet undergoes great physical changes, which finally affect the stability of its structure: it can no longer hold together: parts of it take independent orbits around the sun, having great resemblance to the orbit of the parent comet. With periodical comets, this process is repeated at each successive approach to the sun. Gradually the products of disintegration are distributed along the comet's...o...b..t, and if the earth's...o...b..t cuts this, the phenomenon of shooting-stars is produced."

[26] _Astr. Nach._, Nos. 1710, 1711. For a fuller statement of Schiaparelli's theory, see Silliman's Journal for May, 1867.

These views of the distinguished astronomer of Vienna are confirmed by the star-shower of November 27, 1872. That the orbits of the earth and Biela's comet intersect at the point pa.s.sed by the former about the last of November, and that in 1845 the comet separated into two visible parts, has been stated in a previous chapter. The comet's non-appearance in December, 1865, and in September, 1872, was regarded by astronomers as presumptive evidence of its progressive dissolution. A meteoric shower, resulting from the earth's collision with the cometary _debris_, was accordingly expected about the 27th of November.

The first indication of the approaching display appeared on the evening of November 24, when meteors in unusual numbers were observed by Professor Newton, at New Haven, Connecticut. On Wednesday evening, the 27th, from the close of twilight till 8 o'clock, a decided shower of shooting-stars was noticed in various parts of the United States. At Greencastle, Indiana, Professor Joseph Tingley counted 110 meteors in 40 minutes, and at Princeton, in the same State, Mr. D. Eckley Hunter counted 70 in 80 minutes. The numbers seen at New Haven were considerably greater. The fact that the display commenced before daylight had entirely closed seemed to indicate that only the termination of the shower had been observed in this country. Accordingly the display was soon found to have been witnessed from 60 E. to 90 W.

of Greenwich, or through 150 of longitude. In England the first bolide of the swarm was seen by M. M. Brinkley, at 3 o'clock, P.M., in full daylight. The meteors were most numerous in the southern part of the continent, particularly in Italy. At the Observatory of Breslau, according to M. Faye, 3000 were seen from 6h. 30m. to 7h. 50m. Dr. Heis reported that at Munster 2500 per hour were counted by two observers. At Naples, Signor Gasparis observed two meteors per second. At Turin, M.

Denza, Director of the Observatory, reported 33,400 in 6h. 30m.; many of various and delicate colors, and followed by long and brilliant trains.

At some points the numbers were so great that an accurate enumeration was wholly impossible. In short, the display was decidedly the most brilliant that has occurred since that of November 13, 1833.

But some of the most interesting circ.u.mstances in connection with the phenomena of November 27, 1872, remain to be detailed. Astronomers without exception regarded the display as due to the earth's pa.s.sage through the _debris_ following in the path of Biela's comet. In accordance with this view Dr. Klinkerfues, of Gottingen, concluded that the comet itself, or rather its largest portion, ought to be found in the region of the heavens nearly opposite to that from which the meteoroids appeared to radiate.[27] As this point in the southern hemisphere could not be observed in Europe, he conceived the happy idea of detecting the fugitive _by means of the electric telegraph_. The following was accordingly dispatched to Mr. Pogson, Director of the Government Observatory at Madras, in Southern India: "_Biela touched earth on 27th; search near Theta Centauri_." The first two mornings after the receipt of this dispatch were cloudy at Madras. On the third, however, the cometary fragment was found, and its motion accurately measured. The observer described it as circular and rather bright, with no traces of a tail. But one fragment could be detected. On the next morning, December 3, the comet was again observed. Its diameter had sensibly increased; it had a bright nucleus, and still presented a circular aspect. A faint tail was also noticed, equal in length to one-fourth of the moon's apparent diameter. The following mornings being again cloudy, no further observations could be obtained. This cometary ma.s.s will be in close proximity to the earth about the last of November, 1892. Another brilliant meteoric shower may therefore be expected at that epoch.

[27] The radiant of the Biela meteors is near _Gamma Andromedae_.

The Meteors of April 20.

Meteoric showers have occurred about the 20th of April in the following years:

B.C. 687 15 A.D. 582 1093 } 1094 } 1095 } 1096 } 1122 } 1123 } 1803

The probability that these meteors are derived from a ring which intersects the earth's...o...b..t, was first suggested by Arago in 1836. A comparison of dates led Herrick to designate 27 years as the probable period of the cl.u.s.ter. In the _Astronomische Nachrichten_, No. 1632, Dr.

Weiss called attention to the fact that the orbit of the first comet of 1861 very nearly intersects that of the earth, in longitude 210--the point pa.s.sed by the latter at the epoch of the April meteoric shower. A relation between the meteors and the comet, indicating an approximate equality of periods, was thus suggested as probable. But the comet, according to Oppolzer, does not complete a revolution in less than 415 years. If, therefore, the meteoric period is nearly the same, the known dates of star-showers indicate a diffusion of meteoroids around one half of the orbit previous to the display of the year 15 B.C. No subsequent perturbation, then, of a particular _part_ could sensibly effect the general orbit of the stream. The infrequency of the display renders, therefore, the hypothesis of a long period extremely improbable.

The entire interval between 687 B.C. and A.D. 1803 is 2490 years, or 92 periods of 27.0652 years; and the known dates are all satisfied by the following scheme:

B.C. 687 to B.C. 15 .. 672 years = 25 periods of 26.8800 _y._ each.

15 to A.D. 582 .. 597 " = 22 " 27.1363 "

A.D. 582 to 1095 .. 513 " = 19 " 27.0000 "

1095 to 1122 .. 27 " = 1 " 27.0000 "

1122 to 1803 .. 681 " = 25 " 27.2400 "

With a period of 27 years, the perihelion being interior to the earth's...o...b..t, the aphelion distance of the meteors would be very nearly equal to the distance of Ura.n.u.s. The next shower, if the a.s.sumed period be correct, ought to occur about 1884. It is worthy of remark that near the time of the last (hypothetical) return Mr. Du Chaillu witnessed the meteors of this epoch, in considerable numbers, in the interior of Africa.

The Meteors of December 12.

Meteoric showers have occurred about the 12th of December in the following years:

1. A.D. 901. "The whole hemisphere was filled with those meteors called falling-stars from midnight till morning, to the great surprise of the beholders in Egypt."

2. In 930 a remarkable shower of falling stars was observed in China.

3. Extraordinary meteoric phenomena were observed at Zurich at the same epoch in 1571.

4. On the night of the 11th and 12th of December, 1833, a great number of shooting-stars were seen at Parma. At the maximum as many as ten were visible at the same time.

5. (Doubtful.) 1861, 1862, and 1863. Maximum probably in 1862. The meteors at this return were far from being comparable in numbers with the ancient displays. The shower, however, was distinctly observed.

R. P. Greg, Esq., of Manchester, England, says the period of December 12, 1862, was "exceedingly well defined."

These dates indicate a period of about 29-1/8 years. Thus:

901 to 930 1 period of 29.000 years.

930 to 1571 22 periods of 29.136 "

1571 to 1833 9 periods of 29.111 "

1833 to 1862 1 period of 29.000 "

Meteors of October 16-20.

Meteoric showers were observed from the 16th to the 20th of October in the years 288, 1436, 1439, 1743, and 1798. These dates render it somewhat probable that the period is about 27-1/2 years. Thus:

A.D. 288 to 1439 42 periods of 27.405 years each.

1439 to 1743 11 " 27.636 " "

1743 to 1798 2 " 27.500 " "

If these periods are correct, it is a remarkable coincidence that the aphelion distances of the meteoric rings of April 20, October 18, November 14, and December 12, as well as those of the comets 1866 I., and 1867 I., are all nearly equal to the mean distance of Ura.n.u.s.