Our Astronomical Column

Abstract

TEMPEL'S COMET, 1867 II.—Now that Brorsen's comet of short period is again under observation, the next comet of the same class to be sought for, is that discovered by Dr. Tempel at Marseilles, on April 3, 1867, which was also observed at its next appearance in 1873; it is probable there may be greater difficulty in recovering this object, than appears to have been the case with Brorsen's comet, the reason for which may be made clearer if we briefly detail its history since the year 1867. Less than a month after it was discovered in that year the deviation of the orbit from a parabola became evident, and several of the German astronomers, Prof. Bruhns, now Director of the Observatory of Leipsic, in the first instance, deduced elliptical orbits, with periods of between five and six years. The most complete investigations on the motion of the comet in this year were due to Dr. Sandberg and Mr. Searle. The comet was observed by Dr. Julius Schmidt at Athens till August 21, and the perihelion passage having taken place on May 23, a considerable arc of the orbit was included within the limits of visibility. Dr. Sandberg, after taking into account the effect of planetary perturbations during the comet's appearance, found the period of revolution 2,080 days. On examining the track of this body with reference to the orbits of the planets, it was seen that near the aphelion it must approach very near to the orbit of Jupiter, the least distance being within 0.37 of the mean distance of the earth from the sun, and from the position of this great planet near the time of aphelion passage of the comet early in 1870, it was obvious that great perturbations in the elements of the latter must ensue, and without at least an approximate knowledge of their amount, there might be difficulty in recovering the comet at its next return to perihelion. The first publication of results in this direction was by Mr. W. E. Plummer, from Mr. Bishop's observatory, Twickenham, in February, 1873, followed shortly afterwards by particulars of similar independent investigations undertaken by Dr. Seeliger, of Leipsic, and the late Dr. von Asten, of Pulkowa. It was found that the effect of the attraction of Jupiter, which planet was only 0.32 distant from the comet on January 20, 1870, caused a retrograde change in the longitude of the node to the amount of 221/2°, and increased the inclination of the orbital plane to the ecliptic nearly 3°; the period of revolution was lengthened by more than three months, and the point of nearest approach to the sun was removed further from him by upwards of 0.2 of the earth's mean distance. Changes in the elements to this amount would of course entirely alter the track of the comet in 1873, but they had been so closely determined, that immediately after receiving an ephemeris in which their effect was included, M. Stephan re-detected the comet at Marseilles, and as early as April 3, or five weeks before the perihelion passage, and it was observed until the last week in June. subjoin Dr. Sandberg's elements for the two appearances:—