  The long-term brightness evolution of the great comet C/1995 O1 (Hale-Bopp)
presented a remarkable opportunity to study the behavior of its coma over four
years. We used approximately 2200 total visual magnitudes published in the
International Comet Quarterly taken from 17 observers during the period of 1995
July - 1999 September to create a secular lightcurve. In order to account for
observer differences, we present a novel algorithm to reduce scatter and
increase precision in a lightcurve compiled from many sources. It is
implemented in a publicly available code, ICQSPLITTER. This code addresses the
differences among observers by using a self-consistent statistical approach,
leading to a sharper lightcurve, and improving the precision of the measured
slopes. To first order, the comet's lightcurve approximately follows a r$^{-4}$
response for both pre- and post-perihelion distances. Interestingly, the
pre-perihelion data are better fit with a fifth-order polynomial with
inflection points at 4.0, 2.6, 2.1 and 1.1 au. We analyze these specific
regions and find that they are associated with physical phenomena in the
comet's evolution. Contrary to other reports, the lightcurve shows no evidence
for the comet having been in outburst at discovery. Afrho values derived from
the visual lightcurve data are consistent with a r$^{-1.5}$ dependence on
heliocentric distance, which is similar in shape to those derived from
spectroscopy and narrow-band photometry. We present correlation equations for
visual magnitudes and CO and H2O production rates, which are consistent with
the pre-perihelion visual magnitudes increasing almost entirely due to CO
outgassing until a heliocentric distance of about 2.6 - 3.0 au. We also present
two correlation equations that should prove highly useful for observation
planning and data analysis, and can be generalized to be applicable to other
comets.
