Once you’ve encountered this puzzle, you might start noticing other strange things about calendars:
The Missing Year Zero
As we saw, the BC/AD calendar jumps straight from 1 BC → 1 AD.
If that seems odd, it’s because zero as a number was not widely recognized in Europe when the calendar era was established.
It wasn’t until later that zero became part of our number system.
Astronomical Year Numbering
Interestingly, astronomers do use a year zero:
In that system, 1 BC becomes year 0.
2 BC becomes year –1.
3 BC becomes year –2.
This makes mathematical calculations easier, but it isn’t used in everyday calendars.
Different Calendars Around the World
Of course, the Gregorian calendar isn’t the only calendar:
Islamic Calendar
Hebrew Calendar
Chinese Lunar Calendar
Ethiopian Calendar
… and many others.
