Why Making a Calendar is So Hard

The most natural unit of time on earth is the day. The year is very important for growing food and planning winter survival -but not everywhere. The moon is a strong visual symbol for the passage of time, too. But those three indicators of time do not sync up with each other. Still, people tend to want to keep up with what time of year we are in, so cultures in different parts of the world came up with their own calendars, and they vary quite a bit. (via Digg)