Why leap in February 2023?
Leap February appears because the month after February of the lunar calendar only has the solar term "Qingming", and the neutral "Grain Rain" after Qingming falls to the next month. Therefore, the month without neutral gas appears after February. Therefore, the neutral month after February is named "leap February" after February, which is the reason for leap February.
The lunar calendar is actually a kind of "yin-yang combined calendar" with the same calendar as the lunar calendar and similar calendar years as the solar calendar. It is based on the moon's profit and loss cycle as the calendar month, and also needs to consider the annual solar terms. For example, one year's New Year was spent in the snow, 17 years later, it will be a New Year's Eve. Using such a calendar naturally cannot meet the needs of agricultural production. Therefore, the lunar calendar in China has been in parallel with the 24 solar terms since the Qin and Han Dynasties, and the 24 solar terms are used to guide agricultural production.
Historical evolution of leap month
The position of the lunar leap month is completely artificial from ancient times to the present, and the position of the leap month is different in different calendars of past dynasties. Before the Qin Dynasty, some local calendars put the leap month at the end of a year, which was called "March". The leap month in the early Han dynasty was placed after September, which was called "post-September". In the first year of Emperor Wu of the Han Dynasty, leap months were inserted in every month of the year. Later, it was stipulated that "the month without neutral gas was the leap month of the previous month", which is still in use today.
BC 104 (the first year of Emperor Wu of the Han Dynasty), Emperor Wu found that the previous Zhuan Xu calendar was no longer applicable, so he reformed the calendar and published the new calendar "taichu calendar" in May this year. Taichu calendar corrected the month as the first year (October of the first year of Qin Dynasty), with 29.53 days in January and 354.36 days in a year. This was the most advanced calendar in the world at that time, and it was also the first great reform in China's history.