  Neptune has brightened by more than 10% during the past several decades. We
report on the analysis of published Johnson-Cousins B and V magnitudes dating
back to 1954 along with new U, B, V, R, Rc, I and Ic photometry that we
recorded during the past 24 years. Characteristic magnitudes, colors and
albedos in all seven band-passes are derived from the ensemble of data.
Additionally, 25 spectra spanning 26 hours of observation on 5 nights are
analyzed. The spectrophotometry demonstrates that planetary flux and albedo is
inversely related to the equivalent widths of methane bands. We attribute the
changes in band strength, flux and albedo to the high altitude clouds which
rotate across the planet's visible disk. Bright clouds increase albedo and flux
while reducing methane absorption. Synthetic V magnitudes derived from the
spectroscopy also agree closely with the photometric quantities, which
cross-validates the two techniques. The spectroscopic and photometric results
are discussed within the framework of the secular brightness variations of
Neptune.
