J. Brit. Astron. Assoc., 107, 4, 1997, p. 172-173

Saturn in 1996

Images of Saturn by Isao Miyazaki using a 400mm refl. and Lynxx PC CCD with NR400 filter, taken on 1996 September 22, approximately 1 hour apart.

As previously reported in the Journal, no sooner was Saturn established in the morning sky last summer than sharp-eyed observers reported active weather systems visible as white spots on the planet, notably in the Equatorial Zone (South). Careful observation of these spots, transit estimates in particular, provides a tool to monitor the powerful winds which drive the pastel-hued clouds of the planet. Over recent years, we have been privileged to witness several episodes in which Saturn appears to have been unsually active, these being the apparitions of 1990 (the year of the Great White Spot), 1994, and now 1996 can be added to the list. This interim report extends the record of events through September and October 1996, two months which saw a flow of data submitted to the Section unprecedented since 1990, and is based on the work of Hideto Asada, Arthur Bowyer, Tom Dobbins, David Graham, David Gray, Lee Macdonald, Richard McKim, Masatsugu Minami, Isao Miyazaki, Don Parker, David Weldrake and John Rogers. The contribution of several other observers for whom space precludes a mention by name, is also acknowledged. Plotted on a drift chart it is possible to identify one major site of activity and a number of lesser ones, which persisted for at least several weeks in the EZ(S).... [the report in the Journal continues with detailed information on the observations.]

The 1996 episode may now be compared with activity followed in the EZ(N) during the apparitions of 1994 and 1995. The 1994 storm system displayed a rotation period of 10h 21m 37s for the period Sep 27 to Nov 1. Three white spots tracked through the summer and early autumn of 1995 had respective periods of 10h 21m 50s, accelerating to 10h 20m 52s (1995 spot 'A'), 10h 22m 6s (1995 spot 'B') and 10h 20m 27s (1995 spot 'C'). It is obvious the relatively slow rotation observed in the EZ(N) in 1994 and 1995 was reflected in the EZ(S) in 1996. The accepted System One rotation period for Saturn is 10h 14m but for the last three apparitions, the observed rotation periods of storm-systems in the Equatorial Zone have been at variance with it. Have we witnessed a change in the velocity of Saturn's equatorial jetstream, or is an observed rotation period dependent on the altitude of the storm-cloud in Saturn's atmosphere?

On a scale of magnitude, though not rivalling the Great White Spot of 1990, the repercussions of which went on to encircle the EZ, the 1996 outbreak did surpass that of 1994 and to my knowledge the only record of it appears to be that gathered by the amateur community. With the ringed planet a morning object this summer, one can only wonder what the 1997 apparition may have in store.

David Graham, Director, Saturn Section


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