Change in Rotation Period of Jupiter's Decameter Radio Sources

Data are presented that tend to refute the hypothesis that Jupiter's decameter radio sources have a constant period. Preliminary analysis of 22.2-Mc/ sec observations made at Bethany Observing Station of the Yale Observatory in 1962 and 1963 indicates that the rotation period of the radio sources has lengthened approximately 0.8 sec. Review of the number of occurrences of Jupiter activity for each 5 deg interval of System III (1957.0) longitude of central meridian for the years 1961, 1962, and 1963 (to July 7) reveals a progressive drift in longitude of the major peak of about 10 deg per year. This corresponds to the 0.8 sec lengthening of the period. On a Whittaker periodogram plot of the same material for a variety of assumed periods, the 0.8 sec lengthening is clear and not explainable by statistical fluctuation. Observations of the red spot motion are discussed in view of the decameter result reported herein. (H.M.G.)