Our Astronomical Column

Abstract

ENCKE'S COMET IN 1881.—So far as can be judged without the calculation of the perturbations since 1878 this comet will again arrive at perihelion about November 8 in the present year. In 1848, when the comet passed this point of its orbit on November 26, it was detected with the 15-inch refractor at Cambridge, U.S., on August 27, as “a misty patch of light, faint and without concentration: its light coarsely granulated, so that were it not for its motion it might be mistaken for a group of stars of the 21st magnitude”(Bond). The theoretical intensity of light at this time was 0.21, and we find that, assuming the perihelion passage to occur on November 8, the comet should have this degree of brightness soon after the middle of August next, so that it may be anticipated observations will be practicable with the waning moon about the 20th of that month. The last perihelion passage took place on July 26, 1878, the period of revolution at that time being 1200.58 days according to the late Dr. von Asten. The aphelion distance is 4.0879, the perihelion distance 0.3335, and the minor semi-axis 1.1675 (the earth's mean distance from the sun = 1). The approach to the orbit of the planet Mercury is still very close (0.031) in about 126°.5 heliocentric longitude. The nearest approximation of the two bodies that has occurred since the discovery of the comet's periodicity took place on November 22, 1848, when their distance was only 0.038. It is known that from his investigations on the motion of Kneke's comet, von Asten inferred a much smaller value for the mass of Mercury than had been previously assigned, viz. 1/7636440.