  We present new analyses of the photometric lightcurve of Comet 1P/Halley
during its 1985/86 apparition. As part of a world-wide campaign coordinated by
the International Halley Watch (IHW), narrowband photometry was obtained with
telescopes at 18 observatories. Following submissions to and basic reductions
by the Photometry and Polarimetry Network of the IHW, we computed production
rates and created composite lightcurves for each species. These were used to
measure how the apparent rotational period (~7.35 day), along with its shape,
evolved with time during the apparition. The lightcurve shape systematically
varied from double-peaked to triple-peaked and back again every 8-9 weeks, due
to Halley's non-principal axis (complex) rotation and the associated component
periods. Unexpectedly, we found a phase shift of one-half cycle also took place
during this interval, and therefore the actual beat frequency between the
component periods is twice this interval or 16-18 weeks. Preliminary modeling
suggests that a single source might produce the entire post-perihelion
lightcurve variability and associated evolution. The detailed evolution of the
apparent period varied in a non-smooth manner between 7.2 and 7.6 day, likely
due to a combination of synodic effects and the interaction of solar
illumination with isolated source regions on a body in complex rotation. The
need to simultaneously reproduce each of these characteristics will provide
very strong additional constraints on Halley's component periods associated
with its complex rotation. To assist in these and future analyses, we created a
synthetic lightcurve based directly on the measured data. We unexpectedly
discovered a strong correlation of ion tail disconnection event start times
with minima in the comet's gas production, implying that a decrease in
outgassing is another cause of these events.
