What do you mean by "three Yang Kaitai"?

In the traditional calendar, besides heavenly stems and earthly branches, there are months and dates, and even hours. Spring is the season when everything germinates. The first month is the first month of spring, and the ground branch is yin. When the earthly branch is based on Yin-Yang and Five Elements, Yin belongs to wood and is Sanyang (the child is November of the lunar calendar, the month of winter solstice, called Yiyang). After Shao Yong matched the sixty-four hexagrams with the month and solar terms in the Song Dynasty, he made the following statement:

"Sanyang" means the beginning of spring. The Book of Changes calls Yang Yi nine, ranking ninth, second ninth, third ninth and third third. Yi gua, "October is Kun gua, the image of pure yin; November is a complex divination, and one yang is born in the next; December is divination, and Er Yang is born next; The first month is Thai hexagrams, and Sanyang was born in the next. " The winter solstice in November of the lunar calendar is the shortest day. After that, the days become longer, the yin gradually disappears, and the yang begins to grow. This is the so-called winter solstice. The sun was born in1February 2, and the sun was born in the first month. In the first month, it's a three-yang begets Thai hexagrams. It is both beginning of spring and New Year's Day. Winter goes and spring comes, yin and yang ebb and flow, and everything recovers, so "Three Yang Kai Tai" or "Three Yang Jiao Tai" has become an auspicious language for people to wish each other at the beginning of the year.