The American Journal of Science/Series 3, Volume 22/Observations on the Comet 1881 b

XXVII.—Observations on the Cornet 1881 b; by.

of the sudden appearance of a great comet in the northern sky first reached me through the local newspapers on June 23; but that night was cloudy. On the evening of June 24, the comet was occasionally seen for a few moments at a time, through intervals in clouds, but never with sufficient clearness to admit of satisfactory examinations as to its physical appearance. One micrometric comparison between the comet and DM 50° 1225 was secured with the thirteen-inch refractor. The comet was plainly visible to unassisted vision in a clear sky at sixteen hours mean time, and then appeared as bright as Capella.

Owing to an accident which happened to the equatorial during my absence, I have thus far been unable to secure additional micrometric comparison by that instrument. At lower culmination the comet has usually been hidden by clouds, and the hour is now very inconvenient; so that I can report only the following observations of apparent position:

From the first three positions reduced to 1881·0 and corrected for parallax and aberration by means of values of Δ from a preliminary orbit, I derived the following parabolic elements.

Middle place, C-O. Δλ cos β, +4″. Δβ, -7″. We also have with the same elements: July 8, C—O. Δλ cos β, +30″. Δβ, -75″. The elements therefore are not likely to be found greatly in error.

The similarity of the elements of this comet with those deduced by various computers for the comet of 1807, has already been much discussed in the newspapers. The difference of about three degrees in the position of the nodes, and especially the great difference in the respective values of q (which amounts to ·087) seems larger tlfan can well be ascribed to errors of computation, or possible planetary disturbance.

It seems to me more likely that these two comets may have formed parts of the same body in distant ages, and that these parts may have separated as Biela's comet did. The two parts would need to have but slightly differing mean distances from the sun in order eventually to reach the amount of separation which now exists between the perihelion passages of the 1807 and 1881 comets. A great number of similar, though generally less striking resemblances among cometic orbits have been noted, in cases where absolute identity between the two comets considered seems impossible. These cases increase the demand for a general explanation, such as I have suggested above. The resemblances seem to be too close and too frequent to be considered the result of chance; and the above hypothesis seems to have some support in reason and experience. If the comet of 1881 proves to have a periodic time between one and two thousand years the plausibility of this hypothesis will be very much strengthened.

I have been too much pressed with other duties to give close or systematic attention to the physical characteristics of the comet. The nights of June 26, June 28, July 1, 8 and 13 were unusually favorable for such studies here. The atmosphere was unusually transparent on June 26 and I then traced the tail for a distance of nearly forty degrees from the nucleus. On that night there were two branches. The longer and brighter branch was perfectly straight. The other curved, with its concavity toward greater right ascension. On the next clear night (June 28) the straight branch was of about the same length as the curved one, and was a thin and scarcely perceptible streak. On July 1, the two branches seem to have merged into one, presenting a shorter and broad fan-like appendage, perfectly straight and strongly marked on the preceding side, concave and nebulous on the following.

On all occasions the nucleus under a power of 250 has seemed to be quite distinctly defined and star-like in appearance. On June 26, its measured diameter was 7″; on July 8, this had become 2″. The latter measure reduced to the distance of June 26 becomes 3″·3, a rather surprising reduction in the diameter, if it be real.

Dudley Observatory, Albany, N. Y., July 19, 1881.