2020 is 2 1 century, and 2 1 century is the period from 200 1 to 2100+/. Christianity takes the year when Jesus was born as the Gregorian calendar year, and both BC and AD take this as the standard. Since 1949, China has used the Gregorian calendar and the AD, which are commonly used in most countries of the international community, as its calendar and calendar year.

The origin of advertising calendar:

After Christianity gained dominance in Europe, it faced the problem of determining religious festivals. Among them, Easter is the most important festival As long as Easter is confirmed, other festivals will be confirmed. However, in Christian countries at that time, the date of Easter was different. In this case, in 532 AD, Constantine the Great presided over a very important religious conference-the Nicaean Conference. One of the important tasks of this meeting is to unify the Easter date. The meeting gave this task to the Alexandria Church, which was located at the World Astronomical Center at that time. The Church of Alexandria made a table, but the church was still not satisfied, so the Pope sent a Syrian astronomer, Dionysus, to make further revisions on the table. In the process of revision, Dionysus was not satisfied with the chronology used by the Alexandria Church, which was the chronology of Emperor Diocletian, the eastern Roman emperor, and the year when Diocletian ascended the throne was the starting point of the chronology. Because Diocletian was a heretic and persecuted Christians, he was going to replace the chronology of Emperor Diocletian with a new chronology. So he took the year when Jesus was born as the starting point. It is estimated that this year is the 532nd year after the birth of Jesus. This presumption was gradually popularized by the church and gradually became the chronicle of the world.