Our Astronomical Column

Abstract

ROTATION OF JUPITER.—Most of the determinations of the rotation period of Jupiter have been made by observations of surface markings between latitudes 45° N. and 35° S., and little has been known as to the conditions of rotation near the poles. This is due to the fact that conspicuous and sufficiently definite spots are chiefly confined to the equatorial regions of the planet, and partly to the unfavourable conditions under which the poles are presented to us. Some important observations, however, bearing on the rotation in high latitudes, have been secured by Mr. Stanley Williams with the aid of a 6½-inch Calver reflector (Asi. Nach., 3325). On October 10, 1892, a short dusky streak, almost oblong in appearance, was observed quite close to the north limb of Jupiter, and reaching at least as far as 85° N. Other streaks of similar appearance were subsequently observed, and frequent observations of the times of mid-transit were made. Confirmation of the results has been obtained by an examination of several photographs of the planet taken at the Lick Observatory about the same period, the markings being sufficiently distinct for measurement. Generally speaking, the visual agree very closely with the photographic results, the mean rotation period derived by the two processes only differing by about two seconds. The mean result for the rotation period of the surface material of Jupiter, between north latitudes 40° and 85°, is 9h. 55m. 38˙9s. ± 1˙20s., this being the length of a sidereal rotation expressed in mean solar time. The following statement illustrates the degree of accuracy obtained:—