When does autumn begin and end?

Astronomical:

In the northern hemisphere of Earth, Fall begins on the Autumnal equinox (22-23 September) (in Persian calender it will begin at the first day of Mehr) and ends on the Winter solstice (21-22 December).

In the southern hemisphere of Earth, Fall begins on the Autumnal equinox (20-21 March) and ends on the Winter solstice (20-21 June).

Climatological:

The World Meteorological Organization officially mandates September 1 of any year as the first day of the climatological autumn and November 30 as the last day in the northern hemisphere.

In the southern hemisphere, the climatological autumn begins March 1 and ends May 31.

Ecological:

The ecological autumn has no fixed dates but coincides with the period that the leaves of deciduous trees change color and fall to the ground.