This is a question I have had since the turn of the millennium. Does the new decade begin on January 1, 2020, or 2021?
After researching the question back in 2000 and 2010, I have come to a conclusion: the new decade beings January 1, 2021.
Here is the reasoning: The beginning of the current calendar, the very first day of the Current Era (CE) or Anno Domini (AD) was January 1,1 and ended on December 31, 10. There was no zero in the Roman, Julian or Georgian calendar systems. This would mean that the current decade will end on December 31, 2020.
It is worth noting that the calendar year does not start on day zero, but on day one, January 1.
The problem comes with how we refer to the decades. We speak of the 60s, 70s, 80s, etc. We believe that a person born in 2000 is not a child of the 90s. The argument continues that we are going into the 20s on January 1, 2020, and the Teens ends on December 31, 2019.
Now, this is not an earth-shattering problem but one of personal interest and some confusion as to which calendar we are using in the Western world.
The original Roman calendar was based on the lunar cycle. It was replaced by the Julian calendar in 45CE, based on time and date. The Georgian calendar was established in 1582CE is based on the full orbit of the earth around the sun.
According to aYouGov.com survey “64% of Americans said the next decade will begin on Jan. 1, 2020, and end on Dec. 31, 2029. But nearly 20% said they weren’t sure – and slightly fewer people (17%) said the next decade won’t start until Jan. 1, 2021.”
Sandi Duncan, the managing editor of The Farmer’s Almanac, told NPR, “The next decade won’t start until Jan. 1, 2021.” She continued, “It’s one of these mathematical conundrums that people can argue about until they’re blue in the face.”
Rick Fienberg of the American Astronomical Society agrees with Duncan, though the Society has not taken an official position on the matter. Others see this as a matter of semantics. But this also rolls over to when is your birthday.
We celebrate the first anniversary of one’s birth one annual cycle past day 1, hour 1, and minute 1 of birth. There is no zero time as a starting point. Does this mean that my 60-birthday represented the last year of the 50s decade? It really depends on how you look at it.
It is worth noting that the designer of the Georgian Calendar, a monk named Dionysius Exiguus, used Roman numerals to depict the years. And those of us who are familiar with Roman numerals know that the Romans did not have zero in their mathematics.
The first recorded zero appeared in Mesopotamia around 3 Before Current Era (BCE). The Mayans invented it independently circa 4 CE. In the fifth century CE, the zero was used in India as a place holder in larger numbers, such as 1001 which is different than 101.
The first use of the zero was first used as a mathematical tool by Italian mathematician Leonardo of Pisain in the 13 century. He had presumably learned about the zero from Arab traders, who presumably adopted them during travels to the Indian subcontinent. However, we find the zero as early as 1202 in European writings.
This is all to say if you celebrated the new decade on January 1, 2020, or are waiting until 2021, you are right.
Have a happy healthy and prosperous 2020!