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V.G. Tejfel (Fessenkov Astrophysical Institute)
Three decades of spectral and photometric observations give us an opportunity to consider the most evident changes in the structure of Saturn’s atmosphere from the measurements in continuum spectrum and in the methane absorption bands. It is especially interesting to compare Saturn’s images in UV (370-390 nm), obtained in 1971 and in 2000 at approximately similar conditions of insolation and visibility have detected significant differences in zonal brightness distribution on Saturn’s disk. . Main difference, which is expressed strongly at the wavelengths shorter 400 nm, is the nonsimilar meridional brightness and reflectivity distribution. In 1971 entire equatorial region was occupied by extensive dark belt Its southern boundary had latitude -15 deg. The reflectivity of this belt was about 25 percent lower than in the lighter temperate belt, which expanded to -63 deg of latitude.The ultraviolet CCD-images and spectra of Saturn in 2000 show the presence of the light but narrower band along equator limited from south by -7 degrees. We measured also from CCD-spectra the methane absorption bands 619, 725 and 798 nm and compared their central depths meridional variations with our spectrometric observations in 1971. These longitudinal variations are similar: in both years we can see maximal absorption on latitudes near -30 deg , sharp decrease of absorption in equatorial belt, well expressed decrease on latitudes near -50-60 deg and growth of absorption towards South pole. In 1995, when both hemispheres of Saturn were in equal conditions of insolation and visibility, we registered significant asymmetry in the methane absorption latitudinal distribution, generally similar to observed in 1966: the absorption at northern temperate latitudes is noticeably more than on these latitudes in southern hemisphere. The consideration of all data is in progress now and interested people are invited to join for cooperative analysis of the changes on Saturn during last years.