What changes have taken place in autumn?

First, the natural landscape.

The most obvious change is in trees. Generally speaking, in autumn, most deciduous plants and trees begin to shed their leaves, and the leaves are yellow and curly, falling from the trees and dancing with the wind. It also means that after late autumn and winter, the city will begin to clean up a lot of fallen leaves.

Other ornamental leaves will turn red because they contain a lot of anthocyanins. As a place of photosynthesis, chloroplasts contain not only chlorophyll that makes leaves green, but also carotenoids that make leaves yellow.

In summer, the chlorophyll content in leaves is high, so bright green overshadows yellow. As the temperature drops, the days become shorter and chlorophyll is decomposed in large quantities. At this time, other pigments such as carotenoids submerged in leaves will be exposed.

Second, the temperature:

The temperature will gradually drop in autumn, but it is generally slower than in winter. Due to the difference of dry and wet conditions, there will be cold and rainy weather conditions or dry and cool weather conditions in different regions. In the cold late autumn, due to the large temperature difference between day and night, the water vapor transpiration during the day will condense at night, either dew or frost. Meteorology, when the five-day average temperature is stable below 22 degrees, it is regarded as autumn, and it ends when it is below 10 degrees.

Third, the change of the sun.

In autumn, the direct point of the sun gradually moves south from the northern hemisphere, passes through the equator after the autumnal equinox, and the sun directly shines in the southern hemisphere. Seen from the northern hemisphere, the angle of the sun gradually becomes lower, and the gap between day and night becomes smaller. At the autumnal equinox, the length of day and night is equal. In autumn, the distance between the earth and the sun is from far to near. Seen from the ecliptic plane, the sun is on the background of Leo, Virgo and Libra.

Fourth, other aspects.

In autumn, when the crops are ripe and the fruits are covered with branches, the geese will fly to the warm south in a mighty way.

Extended data:

There are six solar terms in autumn, namely beginning of autumn, Chushu, Bailu, Autumnal Equinox, Cold Dew and First Frost.

Beginning of autumn is the 13 of the 24 solar terms. On August 7th or 8th every year, beginning of autumn is considered as the time when the sun reaches 135. "Autumn" means that summer is cool, which means the beginning of autumn. But in early autumn, the weather in Jianghuai area is still very hot.

Summer is 14 of the 24 solar terms. "Out" means going. In summer, the heat stops here, that is, in summer, the hot summer will pass, the temperature will gradually drop, and the rainfall will gradually decrease.

The autumnal equinox is a solar term representing seasonal changes. On the day of the autumnal equinox, the sun is located at longitude 180 degrees, and the sunlight is almost direct to the equator, and day and night are almost equal. At this time, the waiting temperature in the southern region has generally dropped below 22℃, and it has entered a cool autumn.

Every year1October 8 or 9, when the sun reaches longitude 195, it is cold dew. Cold dew means that the temperature is lower than that of the white dew, and the dew on the ground is colder and will soon condense into frost.

The solar term of the first frost is1October 23rd or 24th every year, 10. In the first frost season, most parts of China enter the dry season, so we should attach great importance to forest protection and fire prevention.

Baidu Encyclopedia-Autumn