Analysis of photometric variations of Uranus and Neptune since 1953

Photoelectric photometry of Uranus and Neptune, obtained between 1953 and 1976, has been analyzed for evidence of planetary variability on various time scales. There is no evidence for either periodic or secular variability at a level of 0.003 mag or greater over intervals of a few months or less, but slow variations of several hundredths of a magnitude have occured for both planets over many years. Variations at the 0.001 mag level may be present on shorter time scales. Solar phase coefficients for both planets are much larger than predicted for clear molecular atmospheres, and the coefficient for Neptune is significantly variable. The lightcurve of Uranus is consistent with a geometrical oblateness of about 0.03, or polar brightening. While the annual mean magnitudes of the planets are highly correlated with one another, no direct correlation with cyclical solar activity is demonstrated.