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During the last week of June 2001, a bright apparition of Neptune's South Polar Feature (SPF) at 70 o S was observed to develop and decay in less than 30 hours, displaying contrast of ~2.5 at 619 nm. Assuming that the same SPF was observed on two consecutive rotations of Neptune, the feature moved eastward at 3.2+/-1.8 o hr -1 (130+/-80 m s -1 ). The SPF made...
We present Stromgren b (472-nm) and y (551-nm) photometry of Neptune based on photoelectric measurements obtained at every apparition from 1972 to 2000. Neptune has brightened by 11% in b and 10% in y since 1980 with most of the increase occurring after 1990. By appending b data to published B magnitudes measured at Lowell from 1950 to 1966 and transformed to b, we show that Neptune is now brighter...
Hubble Space Telescope imaging of Uranus in 1994, 1997, 1998, and 2000 revealed 13 cloud features, allowing the first measurements of wind velocities at northern latitudes not accessible to the Voyager cameras and new measurements of southern-latitude wind velocities determined during the 1986 Voyager encounter. Images acquired with the Keck 10-meter telescope adaptive optics system in June 2000 also...
Recent observations with the Wide-Field Planetary Camera (WFPC-2) on the Hubble Space Telescope (HST) show an unexpectedly rapid change in the atmospheric albedo contrast between the north and south hemispheres. In 1994 at blue wavelengths, the north was around 15% brighter than the south, and was expected to fall to about 12% in 1997, but has dropped to only 6% brighter. At some other wavelengths,...
New measurements of Titan's hemispheric brightness asymmetry from HST images from 260 to 1040 nm show that the contrast is strongest near 450 nm (blue) and, with the opposite sign, at 889 nm (methane band). Comparison with a full Titan year of disk-integrated albedo data indicates that the seasonal cycle in asymmetry is smooth, but is insufficient to explain the variation in albedo, and a twice-per-year...
Solar phase curves for Rhea are presented using new telescopic opposition data along with Voyager imaging observations. Two viable solutions were found to Hapke's model (1986, Icarus 67, 264-280) which was used to describe this phase curve. The porosity derived from the model's opposition parameters show that the optically active portion of Rhea's regolith has a porosity between 80 and 95%, which...
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