Why Is Our Time Considered the 21st Century?

Our calendar is based on the Gregorian calendar.

We live in what is called the 21st century. We recently began the 21st cycle of 100 years, a decade, since the contemporary calendar was started. Looking at it another way, a man who is 18 years old has already begun his 19th year--we have gone through 20 centuries, and are now beginning our 21st. Although many cultures count these centuries differently, the Gregorian calendar, used in the western hemisphere, is the most widely used.

Lunar and Solar Calendars

Calendars are typically constructed around two astronomical phenomena: the phases of the moon and the seasons created by the movement of the sun. The former is approximately 30 days in length, the latter 365.25 days. Since the number of lunar cycles do not easily fit in the number of solar days in a year, various attempts have been made over the centuries to create a calendar that brings them into some systematic form of harmony.

The Gregorian Calendar

The Gregorian calendar used today is a revision of the original Julian calendar. The Julian calander was a huge improvement over the earlier Roman calendar. In the 1500s most European countries adopted the improved Gregorian calendar except for Russia, which held out until the 20th century. The counting of centuries used in the western hemisphere follows the Julian and especially Gregorian calendars.

Other Calendars

Other calendars completely ignore this numbering system, and do not refer to this time as the 21st century at all. For Jews, this is the 5772nd century, for Muslims, it is the 15th century, and for the Chinese, it is the seventy-eighth 60-year cycle.

References

• Calendars through the Ages: History of Our Calendar
• Calendars through the Ages: The Christian Calendar