A. In Jewish law, the year has four tekufot or periods:
1. Tekufat Nisan – the vernal equinox or the beginning of spring in the northern hemisphere,
2. Tekufat Tammuz – the summer solstice or the beginning of summer,
3. Tekufat Tishri – the autumn equinox, and
4. Tekufat Tevet – the winter solstice.
Working on a solar year of 365.25 days (the exact length is 11 minutes, 14 seconds shorter), each tekufah comes 91 days and 7.5 hours after the previous one. The seasons are governed by the solar (i.e. civil), not the Jewish calendar. Thus the solar calendar determines when to say the prayer for rain (v’ten tal umatar). (In the southern hemisphere we do not alter the date for saying the prayer even though our rainy season is six months later.)
We celebrate the gift of rain in the service on Sh’mini Atzeret, but to allow Temple pilgrims time to get home from Jerusalem in dry weather, the Amidah prayer for rain was delayed in Israel for a couple of weeks. In the Diaspora it commences on the 60th day after Tekufat Tishri.