In history, in which period was the Han Dynasty formally established with the first month as the beginning of the year?

In the history of our country, the first month was formally established in the period of Emperor Wu of Han Dynasty.

The beginning of the year refers to the beginning of a year. The earth revolves around the sun for one year, and the "year" belongs to the solar calendar and has nothing to do with the moon. At first, the calendar began with "beginning of spring". When the solar term is beginning of spring, the sun and everything are in spring, which means a new cycle begins. Later, due to the change of the calendar, the New Year usually refers to the first month of the lunar calendar.

New Year's Day is the beginning of a year in the solar calendar. As we all know, China has two parallel calendars, the solar calendar and the lunar calendar. The solar calendar was taken from the west, with the birth of Jesus as the first year, and was implemented in the Republic of China after the Revolution of 1911, with a short history of 100 years. The lunar calendar, also known as the summer calendar, has existed since ancient times. In the process of use, after several revisions, the first month of the year was finally determined.

The greatest influence of changing the calendar was Emperor Wu of the Han Dynasty.