¹ The conditions determining the exact time of the Passover were that the moon must be at the full, the vernal equinox past and the sun in Aries. The fixed date of the feast was the fourteenth day of the first month, Nisan; and if that date was due to fall before these conjunctions the necessary number of days were inserted into the calendar in order to postpone it. Subsidiary causes influencing this intercalation, such as the backwardness of the crops and the beasts, are also mentioned in the rabbinical writings. There was as yet no fixed calendar and adjustments were made each year on an empirical basis.

See Schürer, Hist, of Jewish People, Div. I, Vol. II, Appendix, ‘The Jewish and Macedonian months compared with the Julian calendar’ (Eng. Trans. Edtn. 1890.)