  The historical light curve of the 19th century "Great Eruption" of etaCar
provides a striking record of violent instabilies encountered by the most
massive stars. We report and analyze newly uncovered historical estimates of
the visual brightness of etaCar during its eruption, and we correct some
mistakes in the original record. The revised light curve looks substantially
different from previous accounts: it shows two brief eruptions in 1838 and 1843
that resemble modern supernova impostors, while the final brightening in
December 1844 marks the time when etaCar reached its peak brightness. We
consider the timing of brightening events as they pertain to the putative
binary system in etaCar: (1) The brief 1838 and 1843 events peaked within weeks
of periastron if the pre-1845 orbital period is shorter than at present due to
the mass loss of the eruption. Each event lasted only 100 days. (2) The main
brightening at the end of 1844 has no conceivable association with periastron,
beginning more than 1.5yr afterward. It lasted 10yr, with no obvious influence
of periastron encounters during that time. (3) The 1890 eruption began to
brighten at periastron, but took over 1yr to reach maximum and remained there
for almost 10yr. A second periastron passage midway through the 1890 eruption
had no effect. While evidence for a link between periastron encounters and the
two brief precursor events is compelling, the differences between the three
cases above make it difficult to explain all three phenomena with the same
mechanism.
