When did the sunshine in the northeast begin to move south?

2. Northeast China spans the middle temperate zone and the cold temperate zone from south to north, belonging to temperate monsoon climate, with four distinct seasons, warm and rainy summer and cold and dry winter. From southeast to northwest, the annual precipitation decreases from 1000 mm to below 300 mm, and it transits from humid area and semi-humid area to semi-arid area. The high forest coverage in Northeast China can prolong the melting time of ice and snow, and forest snow storage is helpful to the development of agriculture and forestry.

Third, the summer solstice: Beidou points to B, and the solar calendar is 90. When the sun is at the "Summer Solstice Point" at 90 degrees of the yellow meridian, it is almost directly above the Tropic of Cancer, and the sun is the highest in the northern hemisphere at noon. This day is the longest day and the shortest night in the northern hemisphere. From this day on, it entered the hot season, when everything in the world grew most vigorously. Therefore, in ancient times, this day was called the northern solstice, which meant that the sun moved to the northernmost day. After the summer solstice, the sun gradually moves southward, and the days in the northern hemisphere become shorter and the nights become longer.