Tula Sankranti marks the Sun's passage into Tula, the seventh sign of the sidereal zodiac, corresponding to Libra. It is determined by the Sun reaching a longitude of one hundred and eighty degrees against the fixed stars, using the Lahiri ayanamsa, and normally falls in mid-October.
Like the other sankrantis it is a solar event, set by the Sun's ecliptic longitude and not by a tithi or the Moon's phase, which distinguishes it from the lunar-month festivals. The transit instant is converted to local time, so the observed date and the timing of any ritual bath or gift can vary by a day between cities.
In Odisha the day is kept as Tula Sankranti or Garbhana Sankranti, when the first rice of the season is offered to the goddess Lakshmi in the fields. In Karnataka it is observed as Kaveri Sankramana, marking the sacred rising of the Kaveri at Talakaveri, and in the Tamil calendar it opens the month of Aippasi.