20 17 12.9 is the lunar calendar.

20 17 65438+February 9th is 20171October 22nd.

Lunar calendar is the current modern calendar in China, which belongs to the combined calendar of yin and yang, that is, the combined calendar of lunar calendar and solar calendar. According to the change cycle of the moon phase, each moon phase changes to one month, and the reference solar year is the length of one year, 24 solar terms are added, and leap months are set to make the average calendar year adapt to the tropic year.

The combination of lunar calendar and solar calendar in lunar calendar forms the method of combining yin and yang. Because of the use of "Xia Zheng", it was called Li Xia in ancient times. 20 17 65438+February 9th is 20171October 22nd.

Lunar calendar is a new calendar used after 1970, and its years are divided into flat years and leap years, with flat years 12 months and leap years 13 months. Month is divided into big month and small month, with 30 days in big month and 29 days in small month, and the average calendar month is equal to the full moon.

Shuotian is the first day of the lunar month, which means that the first day of each lunar month must be Shuotian. Each lunar month reflects a complete cycle of lunar phase change, so it belongs to the lunar part of the yin-yang calendar. The twenty-four solar terms of the lunar calendar reflect the different positions on the earth's orbit around the sun, that is, the tropic year cycle, so it belongs to the solar calendar part of the lunar calendar.

Gregorian calendar is the universal calendar in the world at present. After the founding of People's Republic of China (PRC), on September 27th, through the China People's Political Consultative Conference, the Gregorian calendar and the AD calendar, which are commonly used in most countries in the world, will be adopted as the legislative calendar. The so-called Gregorian calendar refers to the time required for the sun to orbit the earth once, which is also called the earth's revolution once. The first day of every year is 1, which is the Gregorian calendar.