The 2003 shell event in η Carinae

Near-infrared, JHKL, photometry of η Car is reported covering the period 2000-2004. This includes the 2003 shell event which was the subject of an international multiwavelength campaign. The fading that accompanied this event was similar to, although slightly deeper than, that which accompanied the previous one. The period between these events is 2023 ± 3 d and they are strictly periodic. Their cause, as well as that of the quasi-periodic variations and secular brightening, are discussed. It seems possible that all three types of variability are consequences of the binary nature of the star.