Variability of Neptune

Earth based observers of Neptune found that the planet varies in brightness at various wavelengths in ways that suggest that changes occur in the planet's atmosphere on several different time-scales. Global inhomogeneities in high altitude haze distribution that are stable for several days permit measurements of the planet's rotation period (about 18 hours), but this stability sometimes breaks down, obscuring the diurnal lightcurve. In addition, there is an apparent long term variability of the brightness of Neptune in anticorrelation with the cycle of solar activity. This slow variability of low amplitude may be punctuated by outbursts of high altitude condensation of particles in the atmosphere, whose decay time is several months.