While this sheet was passing through the press, the attention of
astronomers, and of the public generally, was drawn to the fact of
the above Comet passing (on Oct. 18) within nine millions of miles of
the planet Venus, or less than 9/100ths of the earth’s distance from
the Sun. “And (says Mr. Hind, the astronomer), it is obvious that
if the comet had reached its least distance from the sun a few days
earlier than it has done, the planet might have passed through it;
and I am very far from thinking that close proximity to a comet of
this description would be unattended with danger. The inhabitants of
Venus will witness a cometary spectacle far superior to that which has
recently attracted so much attention here, inasmuch as the tail will
doubtless appear twice as long from that planet as from the earth, and
the nucleus proportionally more brilliant.”
This Comet was first discovered by Dr. G. B. Donati, astronomer at
the Museum of Florence, on the evening of the 2d of June, in right
ascension 141° 18′, and north declination 23° 47′, corresponding to
a position near the star Leonis. Previous to this date we had no
knowledge of its existence, and therefore it was not a predicted
comet; neither is it the one last observed in 1556. At the date of
discovery it was distant from the earth 228,000,000 of miles, and was
an excessively faint object in the largest telescopes.
The tail, from October 2 to 16, when the comet was most conspicuous,
appears to have maintained an average length of at least 40,000,000
miles, subtending an angle varying from 30° to 40°. The dark line or
space down the centre, frequently remarked in other great comets,
was a striking characteristic in that of Donati. The nucleus, though
small, was intensely brilliant in powerful instruments, and for some
time bore high magnifiers to much greater advantage than is usual with
these objects. In several respects this comet resembled the famous
ones of 1744, 1680, and 1811, particularly as regards the signs of
violent agitation going on in the vicinity of the nucleus, such as
the appearance of luminous jets, spiral offshoots, &c., which rapidly
emanated from the planetary point and as quickly lost themselves in the
general nebulosity of the head.
On the 5th Oct. the most casual observer had an opportunity of
satisfying himself as to the accuracy of the mathematical theory of
the motions of comets in the near approach of the nucleus of Donati’s
to Arcturus, the principal star in the constellation Bootes. The
circumstance of the appulse was very nearly as predicted by Mr. Hind.
The comet, according to the investigations by M. Loewy, of the
Observatory of Vienna, arrived at its least distance from the sun a few
minutes after eleven o’clock on the morning of the 30th of September;
its longitude, as seen from the sun at this time, being 36° 13′, and
its distance from him 55,000,000 miles. The longer diameter of its
orbit is 184 times that of the earth’s, or 35,100,000,000 miles;
yet this is considerably less than 1/1000th of the distance of the
nearest fixed star. As an illustration, let any one take a half-sheet
of note-paper, and marking a circle with a sixpence in one corner
of it, describe therein our solar system, drawing the orbits of the
earth and the inferior planets as small as he can by the aid of a
magnifying-glass. If the circumference of the sixpence stands for the
orbit of Neptune, then an oval filling the page will fairly represent
the orbit of Donati’s comet; and if the paper be laid upon the pavement
under the west door of St. Paul’s Cathedral, London, the length of that
edifice will inadequately represent the distance of the nearest fixed
star. The time of revolution resulting from Mr. Loewy’s calculations
is 2495 years, which is about 500 years less than that of the comet of
1811 during the period it was visible from the earth.
That the comet should take more than 2000 years to travel round the
above page of note-paper is explained by its great diminution of speed
as it recedes from the sun. At its perihelion it travelled at the rate
of 127,000 miles an hour, or more than twice as fast as the earth,
whose motion is about 1000 miles a minute. At its aphelion, however,
or its greatest distance from the sun, the comet is a very slow body,
sailing at the rate of 480 miles an hour, or only eight times the
speed of a railway express. At this pace, were it to travel onward in
a straight line, the lapse of a million of years would find it still
travelling half way between our sun and the nearest fixed star.
As this comet last visited us between 2000 and 2495 years since, we
know that its appearance was at an interesting period of the world’s
history. It might have terrified the Athenians into accepting the
bloody code of Draco. It might have announced the destruction of
Nineveh, or of Babylon, or the capture of Jerusalem by Nebuchadnezzar.
It might have been seen by the expedition which sailed round Africa
in the reign of Pharaoh Necho. It might have given interest to the
foundation of the Pythian games. Within the probable range of its
last visitation are comprehended the whole of the great events of the
history of Greece; and among the spectators of the comet may have been
the so-called sages of Greece and even the prophets of Holy Writ:
Thales might have attempted to calculate its return, and Jeremiah might
have tried to read its warning.--_Abridged from a Communication from
Mr. Hind to the Times, and from a Leader in that Journal._