✦ Autumnal Equinox ✦
✦ Sun crosses the equator again — day and night equal ✦
✦ What is Autumnal Equinox? ✦
Autumnal Equinox = the day of the year when the Sun crosses the equator from north to south. Day and night are again equal length — 12 hours each. The date is approximately September 22 or 23 each year.
Astronomically, the tropical Sun enters Libra (Tula) on this day. In the Northern Hemisphere, autumn begins astronomically — days begin shortening and nights lengthening. In the Southern Hemisphere, spring begins.
In the Indian Vedic tradition, the sidereal Tula Sankranti falls around October 17 — due to ayanamsha drift. This begins the "Tula month". Sharad Navratri and Dussehra are celebrated in this period — for shakti-puja.
The Autumnal Equinox marks (per some traditions) the end of "deva-kaal" and the beginning of "pitru-kaal". This is the second balance-point of the year — both Vernal and Autumnal equinoxes are days of day-night equality. Nature reflects this balance — the equilibrium of expansion and contraction.
✦ Concept & Rule ✦
Astronomical basis: Around September 23, neither hemisphere tilts toward the Sun. The Sun's rays fall perpendicularly on the equator. From the Northern Hemisphere, the Sun now appears to move southward — days begin shortening. The 6-month night begins at the North Pole. The duration of the Sun's visibility starts decreasing.