There are two interpretations possible for north and south motion, one is movement from solstice to solstice as Vartaka has proposed. Other is movement north of celestial equator and south of celestial equator. This interpretation puts vernal equinox in Krittika. This interpretation is preferred as it is consistent with Vedic literature and Vedanga Jyotisha as well as rest of Taittiriya Brahmana itself. Please do check my next blog on the dating on Taittiriya Brahmana for further details.