Popular Science Monthly/Volume 24/February 1884/The Comet of 1812 and 1883
|THE COMET OF 1812 AND 1883.|
By Professor DANIEL KIRKWOOD.
IN the quarter of a century included between August, 1802, and August, 1827, Jean Louis Pons discovered thirty comets—twice as many as all observers besides. Of this number are the celebrated comets of short period designated as Encke's, Biela's, and Winnecke's, as well as the comet of 1812, now visible on its first predicted return. It was originally detected on the 20th of July, and was the thirteenth discovered by Pons within ten years. Its appearance at first was that of an irregular nebula without tail or beard, and it was only visible through a telescope. By the 14th of September it was easily seen without optical aid; its tail was over two degrees in length, and the diameter of its nucleus was five or six seconds. It continued visible till October—a period of ten weeks—and was consequently well observed. Cooper's valuable work on "Cometic Orbits" contains eight sets of elements by different computers. Encke distinctly recognized the elliptic form of the orbit, and the elements which he assigned have been generally preferred. They are as follows:
|Perihelion passage||1812, Sept., 15·3136, G. M. T.|
|Longitude of perihelion||92° 18' 46"|
|Longitude of ascending node||253° 1' 3"|
|Inclination||73° 57' 3"|
|Period||70 68 years.|
According to Encke, therefore, the next perihelion passage was to have been expected in June, 1883—about three months before the actual discovery of the comet by Mr. W. R. Brooks. A re-discussion of the observations of 1812 had, however, been recently completed by Dr. Schulhof and M. Bossert, whose calculations gave a probable period about seven months longer than that obtained by Encke. The true period is found to be very nearly a mean between these earlier and later estimates.
On its present return the comet was first glimpsed on the night of September 1st, by Mr. William R. Brooks, Director of Red House Observatory, Phelps, New York. He was, however, prevented by clouds from verifying his conjecture of the cometary character of the nebulous speck till the evening of the 3d. Its identity with the comet of 1812 was shown on the 18th of September, by the Rev. Mr. Searles, of New York, and independently on the day following by Professor Lewis Boss, of the Dudley Observatory. The latter designated January 25, 1884, as the date of perihelion passage. Astronomers of the twentieth century will probably witness its next apparition in the summer of 1955.
The comet of 1812 is one of a remarkable group whose periods range between sixty-eight and seventy-six years, all of their aphelia being some distance beyond the orbit of Neptune. It seems, however, to be specially related to the fourth comet of 1846. The latter was discovered by De Vico, at Rome, on February 20th, and independently, by Professor G. P. Bond, February 26th. It remained visible ten weeks, and its elements were calculated by Peirce, Hind, Van Diense, and others. The present writer has elsewhere called attention to the close agreement of the elements of the comets of 1812 and 1846. These coincidences are seen at a glance in the following figure, where the dotted ellipse represents the orbit of the comet of 1812, and the continuous curve that of the fourth comet of 1846.
It seems difficult to regard this general similarity as accidental. A possible explanation may be found in the hypothesis of an ancient comet's separation into parts—a phenomenon known to have occurred in the case of Biela's comet. It has also been pointed out that the paths of both comets very nearly intersect the orbit of Venus; that of 1812 in true anomaly 341°, and that of 1846 in 347°.
On the hypothesis of a common origin it is obvious that these bodies must have entered the solar system at a remote epoch. It seems, therefore, quite remarkable that neither is known to have been observed before 1812. The period of De Vico's comet of 1846 is still too uncertain to be traced backward through former returns; but, with a mean period of the Pons-Brooks comet equal to the interval between the two observed apparitions, we find the dates of former perihelion passages to have been approximately as given below. The nearest corresponding dates at which comets were seen are also appended:
of the comet of 1812.
at which comets
of the comet of 1812.
at which comets
|1670||. . .||1384||1382|
|1598||. . .||1313||1313|
No comets are recorded for 1670 and 1598, and very little is known of those seen in 1742 and 1529. Some of the preceding may have been returns of the Pons-Brooks comet. The comets of 1812 and 1846, as has been shown, are both liable to great perturbation by Venus.
- "Comets and Meteors," Chapter III. The nodal lines are nearly coincident, but the ascending node of the one is at the descending node of the other.