What do you mean by $3900?

Three-Yuan Nine-Luck is a method of dividing time in China. The ancients divided 20 years into one fortune, and three 20 years were three fortunes, forming one yuan. The ternary games are Shangyuan, Zhongyuan and Xia Yuan, and each yuan has three games, which are collectively called "Sanyuan Nine Games".

Shangyuan is the first, second and third luck; The Central Plains is the fourth, fifth and sixth luck; The next yuan is the seventh, eighth and ninth luck. 60-year shipment per yuan, 3 yuan total 180 years. It has been recorded in the Yellow Calendar since ancient times and used in combination with the dry calendar, which is mostly used for geomantic omen.

Among the nine planets in the solar system, Saturn and Jupiter meet once every 20 years and are in a straight line; Saturn, Jupiter and Mercury will meet once every 60 years. Every 180 years, the nine planets will be on the same side of the sun, distributed in a small fan shape, forming a "nine-star connection".

Because the law of motion of this celestial body will never change, astronomers define the time system of "three yuan and nine luck" according to this law, with 180 as the positive element, and each positive element is divided into upper, middle and lower three yuan, each for 60 years, and each element is divided into three luck, that is, one to nine luck.

At the same time, the operation law of Beidou plus the left satellite and the right satellite coincides with the natural phenomena and the good or bad luck of people on the earth, and one plays a leading role every 20 years.

The up and down direction is the universe, the past is the universe, and the universe and the universe refer to space and time respectively. Ancient ancestors looked up at astronomy and down at geography. After a long period of observation, they found that there is some inherent regularity between the running laws of the planets in the solar system and the changing laws of natural and human phenomena on earth, especially the running laws of Jupiter and Saturn have great influence on the earth.

The law of celestial motion goes round and round and never changes. On this basis, through the organic combination of the "Three-Yuan Nine-Games" and the Big Dipper and Jiuqi, which are nine planets, a set of geomantic theory with unified space and time is established and developed. Jupiter orbits the sun for about twelve years, and Saturn orbits the sun for about thirty years.

Jupiter and Saturn meet once every 20 years, and the meeting of the two planets will have various effects on us in ways we don't realize. Therefore, metaphysical scholars have divided a yuan rhyme for 20 years.