1 In autumn, the most obvious changes in the natural landscape are in the trees, as urban society begins to clear away the leaves and the mountains are flooded with tourists who come to see the maple blossoms.

2 Autumn is the transition from summer to winter. On the lunar calendar, it is from July to September when autumn begins to winter, and on the solar calendar, it is from September to November, and astronomically, it is the period from the autumnal equinox to the winter solstice.

3 The main meteorological hazards in the fall are: autumn rains in western China, cold dew winds in the south, frost, and cold temperatures. Generally speaking, in the fall, the sun's altitude angle decreases, the temperature decreases; the autumn breeze is refreshing, the heat subsides, the fruits are full of branches, and the fields are golden.

Autumn is characterized by a slow decline in temperatures from high to high, the leaves of trees turning from lush green to yellow, some turning red, and starting to fall, the grass gradually wilting and turning yellow, and the crops starting to ripen and being harvested.

Expanded:

Autumn is the season of harvest, when the fruits of many plants ripen. In subtropical regions of the Northern Hemisphere temperatures drop significantly in the fall relative to the summer. As temperatures drop, the leaves of many perennial plants will gradually change color, wither, and eventually fall, leaving only the branches to survive the winter. And annuals will reach the end of their lives, withering and dying throughout.

Temperatures drop gradually in the fall, but generally more slowly than in the winter. Due to differences in wet and dry conditions, different regions can experience weather conditions that are cold and rainy, or dry and cool. In the colder late autumn, due to the large temperature difference between day and night, water vapor that transpires during the day will condense at night, either as dew or frost.

Seasons:

The sun is located at 135 degrees of the yellow meridian at the beginning of autumn, and crosses the festival on August 7-9;

The sun is located at 150 degrees of the yellow meridian at the end of summer, and crosses the festival on August 22-24;

The sun is located at 165 degrees of the yellow meridian at the end of white dew and crosses the festival on September 7-9;

The sun is located at 180 degrees of the yellow meridian at the end of autumn and crosses the festival on September 23-24.

The sun is located at 180 degrees of the yellow meridian at the end of autumn;

The cold dew sun is located at 195 degrees of yellow longitude, and the festival is celebrated on October 8-9;

The frost sun is located at 210 degrees of yellow longitude, and the festival is celebrated on October 23-24

The point of direct sunlight gradually moves southward from the northern hemisphere in the fall, crossing the equator after the autumnal equinox, with the sun shining directly on the southern hemisphere. From the northern hemisphere, the angle of the sun gradually becomes lower, and the gap between day and night becomes smaller. At the fall equinox, day and night are equal in length. During the fall, the Earth's distance from the Sun grows closer and closer. From the plane of the ecliptic, the Sun appears to lie in the background of the constellations Leo, Virgo, and Libra.

Among the art works with the theme of autumn, the representative ones are "Evening in the Autumn Countryside," "Knowing Autumn," created by the artist Zhu Xuanhanhan, "Autumn in Yansai," created by Bai Gengyan, "Nineteen Autumns," created by He Jiaying, and "Autumn," one of the torrent trilogy by Ba Jin.

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