  Extensive spectral observations of eta Carinae over the last cycle, and
particularly around the 2003.5 low excitation event, have been obtained. The
variability of both narrow and broad lines, when combined with data taken from
two earlier cycles, reveal a common and well defined period. We have combined
the cycle lengths derived from the many lines in the optical spectrum with
those from broad-band X-rays, optical and near-infrared observations, and
obtained a period length of 2022.7+-1.3 d.
  Spectroscopic data collected during the last 60 years yield an average period
of 2020+-4 d, consistent with the present day period. The period cannot have
changed by more than $\Delta$P/P=0.0007 since 1948. This confirms the previous
claims of a true, stable periodicity, and gives strong support to the binary
scenario. We have used the disappearance of the narrow component of HeI 6678 to
define the epoch of the Cycle 11 minimum, T_0=JD 2,452,819.8. The next event is
predicted to occur on 2009 January 11 (+-2 days). The dates for the start of
the minimum in other spectral features and broad-bands is very close to this
date, and have well determined time delays from the HeI epoch.
