In mid-September, the weather described in this sentence is slight cold.

It describes the weather in mid-September, when the temperature began to drop and the dew condensed into frost.

Slight cold is one of the twenty-four solar terms, which generally appears on the 5th or 6th day of 65438+ 10 every year.

In September, with the end of summer, the weather gradually cooled down. The temperature difference between day and night began to increase, because the direct angle of the sun gradually decreased, resulting in less heat received during the day. It gets colder at night, and dew begins to condense on grass leaves or branches, forming tiny ice crystals. These ice crystals sparkle in the early morning sun, as if the whole world were inlaid with diamonds.

During the slight cold season, the weather is even colder. Although the sunshine can still bring some warmth at this time, the cold at night has become biting. People began to wear thick cotton-padded clothes to resist the cold weather. In the north, the river is already frozen so thick that people can slide freely on the ice. In the south, although the water has not frozen, the river has become cold and is no longer suitable for swimming.

In addition to the cold temperature, there are other phenological phenomena in the slight cold season. For example, plants begin to go into dormancy and grow slowly. Many animals also become less active, and some even go into hibernation. At this time, geese also began to migrate to the south, looking for a warmer climate.

The origin of frost in mid-September;

The phrase "September is cold and dew condenses into frost" comes from the twenty-four solar terms and is an important document in ancient China. This book was written by Huang Chengxian in the Ming Dynasty, and was completed in the 23rd year of Wanli in the Ming Dynasty (AD 1595). Taking the moon as the key link, this book expounds the changing laws of astronomy, meteorology, phenology and agricultural activities on a monthly basis, and is one of the important ancient books on agriculture and phenology in China.

This sentence describes the weather changes in mid-September when the air is cold and dew condenses into frost. Specifically, the neutral qi refers to the white dew in the second of the 24 solar terms. Sue means that the weather is getting cold, and freezing into frost means that dew is freezing into frost. At this time in mid-September, the weather is getting colder and colder, and the dew has condensed into frost.

The weather change described in this sentence is of great significance in ancient China. On the one hand, it marks the deepening of autumn and the further reduction of temperature; On the other hand, it also shows that the growth of crops has entered the final stage, and farmers need to seize the time to harvest crops to avoid being affected by natural disasters such as frost. Therefore, the phrase "it's cold in mid-September and it's frosty" is not only a description of the weather change, but also a guidance and reminder for agricultural production.