OTHER REMARKABLE COMETS.
It remains to describe some of the most remarkable comets of which we
have any record, but of which we have no means of determining with
certainty whether they move in ellipses, parabolas, or hyperbolas.
In the year 466 B.C., a large comet appeared simultaneously with the
famous fall of meteoric stones near Ægospotamos. The former was supposed
by the ancients to have had some agency in producing the latter
phenomenon. Another of extraordinary magnitude appeared in the year 373
B.C. This comet was so bright as to throw shadows, and its tail extended
one-third of the distance from the horizon to the zenith. The years 156,
136, 130, and 48, before our era, were also signalized by the appearance
of very large comets. The apparent magnitude of the first of these is
said to have equaled that of the sun itself; while its light was
sufficient to diminish sensibly the darkness of the night. The second is
said to have filled a fourth part of the celestial hemisphere. The comet
of 130 B.C., sometimes called the comet of Mithridates, because of its
appearance about the time of his birth, is said to have rivaled the sun
in splendor.
In A.D. 178 a large comet was visible during a period of nearly three
months. Its nucleus had a remarkably red or fiery appearance, and the
greatest length of its tail exceeded 60°. The most brilliant comets of
the sixth century were probably those of 531 and 582. The train of the
latter, as seen in the west soon after sunset, presented the appearance
of a distant conflagration.
Great comets appeared in the years 975, 1264, and 1556. Of these, the
comet of 1264 had the greatest apparent magnitude. It was first seen
early in July, and attained its greatest brilliancy in the latter part
of August, when its tail was 100° in length. It disappeared on the 3d of
October, about the time of the death of Pope Urban IV., of which event
the comet, in consequence of this coincidence, was considered the
precursor. These comets, on account of the similarity of their elements,
were believed by many astronomers to be the same, and to have a period
of about 300 years. In the case of identity, however, another
reappearance should have occurred soon after the middle of the
nineteenth century. As no such return was observed, we may conclude that
the comets were not the same, and that their periods are wholly unknown.
The comet discovered on the 10th of November, 1618, was one of the
largest in modern times; its tail having attained the extraordinary
length of 104°. The comet of 1652, so carefully observed by Hevelius,
almost equaled the moon in apparent magnitude. It shone, however, with a
lurid, dismal light. The tail of the comet of 1680 was 90° in length.
This body is also remarkable for its near approach to the sun; its least
distance from the solar surface having been only 147,000 miles. It will
always be especially memorable, however, for having furnished Newton the
data by means of which he first showed that comets in their orbital
motions are governed by the same principle that regulates the planetary
revolutions.
Of all the comets which appeared during the eighteenth century, that
which passed its perihelion on the 7th of October, 1769, had the
greatest apparent magnitude. It was discovered by Messier on the 8th of
August, and continued to be observed till the 1st of December. On the
11th of September the length of its tail was 97°. The comet discovered
on the 26th of March, 1811, is in some respects the most remarkable on
record. It was observed during a period of 16 months and 22 days,--the
longest period of visibility known. On account of its situation with
respect to the earth, the apparent length of its tail was much less than
that of some other comets; its true length, however, was at one time
120,000,000 miles; and Sir William Herschel found that on the 12th of
October the greatest circular section of the tail was 15,000,000 miles
in diameter. The same astronomer found the diameter of the head of the
comet to be 127,000 miles, and that of the envelope at least 643,000. As
a general thing, the length of a comet-train increases very rapidly as
the body approaches the sun. But the perihelion distance of the comet of
1811 was considerably greater than the distance of the earth from the
sun; while its nearest approach to the earth was 110,000,000 miles. Its
true magnitude, therefore, has probably not been surpassed by any other
observed; and had its perihelion been very near the sun, it must have
exhibited an appearance of terrific grandeur. This comet has an elliptic
orbit, and its period, according to Argelander, is 3065 years.
The great comet of 1861 was discovered on the 13th of May, by Mr. John
Tebbut, Jr., of New South Wales. In this country, as well as in Europe,
it was first generally observed on the evening of June 30,--19 days
after its perihelion passage. Sir John Herschel, who observed it in
Kent, England, remarks that it far exceeded in brilliancy any comets he
had ever seen, not excepting those of 1811 and 1858. According to Father
Secchi, of the Collegio Romano, the length of its tail was 118°. This,
with a single exception,[8] is the greatest on record. The computed
orbit is elliptical; the period, 419 years.
[8] The tail of the first comet of 1865 (observed in the
Southern Hemisphere) attained the unprecedented length
of 150°.--_M. N. R. A. S._, vol. xxv., p. 220.