Which solar term in a year begins to lengthen by one day?

After the vernal equinox, the days in the northern hemisphere began to get longer.

"The vernal equinox, Yin and Yang. So it's hot and cold day and night. " It means that the vernal equinox is a solar term, and day and night are equal in length, so day and night are average, and cold and heat are average.

A word "fen" tells the boundary between day and night, cold and heat. At this time, the longitude of the sun is 0 degrees and the position of the sun is above the equator. According to the lunar calendar, "it refers to the vernal equinox, which is about Sunday. The northern and southern hemispheres are equally divided day and night, which is also half of spring, so it is called the vernal equinox."

The vernal equinox usually refers to the moment when the sun's ecliptic is at 0, around February 15 of the lunar calendar and March 20-2 1 of the Gregorian calendar.

At the vernal equinox, theoretically speaking, the length of day and night is equal in most parts of the world, and the special phenomenon that "the sun circles on the horizon all day" can be observed near the North Pole (90 north latitude) and the South Pole (90 south latitude). After the vernal equinox, the days in the northern hemisphere are long and the nights are short, that is, the days in a day are longer than the nights.

Extended data:

Climatic characteristics of vernal equinox;

1, sunshine

On the vernal equinox, the sun shines almost directly on the equator of the earth, and the whole world is almost as long as day and night. After the vernal equinox, the direct point of the sun began to enter the northern hemisphere, and the days became longer and the nights became shorter in all parts of the northern hemisphere. Vernal equinox is an important solar term.

It not only has astronomical significance: the northern and southern hemispheres are equally divided day and night, but also has obvious characteristics in climate. At the vernal equinox, except the Qinghai-Tibet Plateau, the northeast, the northwest and the northern part of North China, China entered a beautiful spring. On the vast land, willows are green, Fei Ying grass grows, wheat jointing and rape blossoms are fragrant.

2. Air pressure conditions

During the spring equinox and solar terms, the East Asian trough is obviously weakened, and the trough ridge activity in the westerly belt is obviously enhanced. From Mongolia to the northeast, there are often low-pressure activities and cyclone development. Low-pressure movement causes cold air to go south, and it is windy and windy in the north. When the long wave trough moves eastward, there will be continuous rainy and cold weather due to the intersection of cold and warm air masses.

3. Temperature and precipitation

During the vernal equinox, the daily average temperature in all parts of China rose steadily to above 0℃ except the alpine mountain area and the area north of 45 north latitude. At this time, the cold has passed and the temperature has risen rapidly, especially in North China and Huanghuai Plain. The daily average temperature rises to above 10℃ almost at the same time as the rainy areas along the Yangtze River and the south of the Yangtze River, entering a bright spring.

On the vast land, on the bank of willow green, the grass grows in Fei Ying, the wheat is jointing, the rape blossoms are fragrant, the peach blossoms are red, and Li Bai is coming in spring. South China is a scene of late spring. According to the climate law, the precipitation in Jiangnan increased rapidly at this time, and it entered the period of "peach blossom flooding" in spring; In the northeast, north and northwest regions where "spring rain is as expensive as oil", precipitation is still very little, so resisting the threat of spring drought is the main problem of agricultural production.

Baidu encyclopedia-vernal equinox