  Spectra (1951-78) of the central object in eta Car, taken by A.D. Thackeray,
reveal three previously unrecorded epochs of low excitation. Since 1948, at
least, these states have occurred regularly in the 2020 day cycle proposed by
Damineli et al. They last about 10 percent of each cycle. Early slit spectra
(1899-1919) suggest that at that time the object was always in a low state.
JHKL photometry is reported for the period 1994-2000. This shows that the
secular increase in brightness found in 1972-94 has continued and its rate has
increased at the shorter wavelengths. Modulation of the infrared brightness in
a period near 2020 days continues. There is a dip in the JHKL light curves near
1998.0, coincident with a dip in the X-ray light curve. Evidence is given that
this dip in the infrared repeats in the 2020 day cycle. As suggested by
Whitelock & Laney, the dip is best interpreted as an eclipse phenomenon in an
interacting binary system; the object eclipsed being a bright region (`hot
spot'), possibly on a circumstellar disc or produced by interacting stellar
winds. The eclipse coincides in phase and duration with the state of low
excitation. It is presumably caused by a plasma column and/or by one of the
stars in the system.
