Abstract:
The observe emersion event of the occulation of the star Hyd -20º51695 by Uranus on 1982 May 1 has been used to evaluate the temperature of the Uranian upper atmosphere. Assuming an isothermal atmosphere the scale height comes out to be 48 ± 7 km which corresponds to an isothermal temperature of 105 ± 16K for the Uranian upeer atmosphere containing 90% hydrogen and 10% helium by number. From the inverted temperature profile, the mean temperature of the Uranian upper atmosphere comes out to be 100 ± 25 K for the altitude range 20 km above to 100 km below the half=light level. A comparison of all available independent determinations of mean atmospheric temperature since 1977 March suggests that the mean temperature of the Uranian upper atmosphere is changing with time. There is an increasing trend during the period 1977 to 1980 and a decreasing trend during the period 1980 to 1982.
