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Published online by Cambridge University Press: 14 August 2015
The brightnesses of Titan and Neptune have been monitored photo-electrically at 472 and 551 nm since 1972 at the Lowell Observatory, yielding annual mean magnitudes accurate to 0.3 percent (0.003 mag). Both objects increased steadily in brightness until 1976 and declined thereafter (Lockwood 1977, Lockwood and Thompson 1979). The range of variation was about 0.08 mag for Titan and 0.03 mag for Neptune.