How to simply tell the children in kindergarten the source of the winter solstice?

According to legend, more than 3000 years ago, the Central Plains of China began to use the soil gauge method (standard table) to measure shadows, and its position in the world was measured in Luoyi, Henan Province, and it was designated as soil. The first of the 24 solar terms determined by Duke Zhou is the "winter solstice" determined by standard chart mapping, and is considered to be the first of the 24 solar terms.

The essence of the method of Surveying Shadows by Soil Gauge is that "the tree is eight feet high, and the scenery is five inches long from summer to the sun (equivalent to no pole on the Tropic of Cancer); On the solstice of winter, the scene is one foot, three feet and five inches long (that is, an eight-foot high benchmark is erected). On the summer solstice, the shadow of noon is 65,438+0.5 feet, and on the winter solstice, the shadow of noon is 65,438+03.5 feet. " Measure the soil depth, correct the shadow, find the ground, and check at four o'clock. "

It is said in Shangshu Luogu that the Duke of Zhou "looked forward to Luoshi" and made some investigations in several places around Luoyang, and finally determined that Jianshui East, Zhuoshui West and Zhuoshui East are all "only Luoshi" (all good places to build ancestral halls). The story of Duke Zhou's choice of Luoyi's base site through "Tuguitu" is recorded in ancient books and regarded by later generations as the law of sealing the country.

Extended data:

Solar term time

Pointing to the bucket, the longitude of the sun is 270, which is the solstice in winter. The first month is the first month, November is the second month, and the winter solstice is the 22nd of the 24 solar terms. The winter solstice usually falls on the second day of Gregorian calendar 65438+February 2 1 or 65438+February 22. For example, the specific time of winter solstice in 2020: 65438+February 2 1, 18: 02.

Note: The average time method (used before 1645) does not consider the uneven speed of the sun moving on the ecliptic, which is different from the constant gas method (used since 1645), and the specific intersection time of each solar term is also different.

Astronomically, the "winter solstice" is the turning point of the sun's southward movement. Because the earth is located near the perihelion in winter, and its running speed is slightly faster, the time of direct sunlight in the southern hemisphere in a year is about 8 days shorter than that in the northern hemisphere, so the winter in the northern hemisphere is slightly shorter than that in summer.