The Red Spot on Jupiter

Abstract

ON August 19, at 14h. 40m., I began observing Jupiter with my 10-inch reflector, power 252. The red spot was seen slightly east of the central meridian, and it looked decidedly fainter and less definite than during the last opposition. The spot was estimated to be precisely central at 14h. 46m., and this is 14.3 minutes in advance of the time given in Mr. Marth's ephemeris (Monthly Notices, May, 1892). The motion of the spot has therefore shown a considerable acceleration during recent months. Between August 2, 1891, and February 2, 1892, the mean rotation period was 9h. 55m. 42.2s, but between February 2 and August 19, 1892, it was only 9h. 55m. 39.3s. This is a difference of 3 seconds, and it clearly proves that the motion of the spot is affected by some remarkable variations. A very decided retardation set in at the end of August, 1891, and continued to operate until February, 1892, but since that time the spot has exhibited an expected celerity of movement.