Question: How do we know what time it is? Like when clocks were invented, how did they know what time to set it at. I know you can tell what time it is around by how the sun is positioned in the sky but how does that give you the exact number?

Ian Stephenson answered on 25 Jun 2014:

The exact way we measure time is pretty random: 2 lots of 12 hours in a day… There’s no specific reason for it other than 12 is a pretty cool number because it divides by lots of other numbers.

What do we HAVE to keep:
well 1 day is how long it takes the earth to rotate.
1 year is how long it takes the sun to go round the earth.

So one year has to be 365 days (plus we need leap years to keep in sync). After that we can make up any system we like.

In fact there have been suggestions that we should move to decimal time, we’d have 1000 millDays (about 1.5 minutes) per day. or 100 centiDays (about 15 minutes). It all works a lot more simply, but it would be just too crazy to change everything over.

Once we’ve decided how many bits to slice a day into, we can identify mid day pretty easily, as thats when the sun is at its highest, and exactly half a day away from that would be midnight.

Weeks are pretty random, but 28 days is a lunar month, and 13 of those (ish) make a year, so actually 13 months per year would be a much better system than the 12 we have at the minute…