The shortest season is autumn, because three autumn days a day. Autumn is one of the four seasons. In the meteorological sense, autumn in the north temperate zone is from August 23 (summer vacation) to November 20 (light snow); The autumn of the southern temperate zone is from February 19 (rain in the northern hemisphere) to May 21 (little full in the northern hemisphere).
The four seasons refer to the four seasons that occur alternately in a year, namely spring, summer, autumn and winter, with three months each season.
The four seasons on earth are first expressed as an astronomical phenomenon, which is not only the periodic change of temperature, but also the periodic change of the length of day and night and the height of the sun. Of course, the length of day and night and the height of the noon sun determine the change of temperature. The gradual change of the four seasons is not unified in the world. The northern hemisphere is summer and the southern hemisphere is winter; The northern hemisphere changes from warm to cold, and the southern hemisphere changes from cold to hot. The length of day and night and the height of the sun vary periodically in different seasons.
In terms of climate, the four seasons are distinguished by temperature. In the northern hemisphere, generally speaking, March May is spring, June August is summer, September November is autumn, and December February is winter.
In the southern hemisphere, the time of each season is just the opposite of that in the northern hemisphere. When the southern hemisphere is summer, the northern hemisphere is winter; When the southern hemisphere is winter, the northern hemisphere is summer. There is no obvious boundary between seasons, and the transformation of seasons is gradual.