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 P _ { \mathrm { pres } } ~ { } = ~ { } 2022.7 \pm 1.3 d .

Spectroscopic data collected during the last 60 years yield an average period of P _ { \mathrm { avg } } ~ { } = ~ { } 2020 \pm 4 d , consistent with the present day period .
The period can not have changed by more than \Delta P/PÂ =Â 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 He i 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 ( \pm 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 He i epoch .