Why are the numbers 12-24 used to tell time?

Answer 1

36

Answer 2

The 12 probably comes about from moon watchers some 5000 or so years ago; the 24 comes from the Babylonians about 4000 years ago and nobody has been able to find a better system.

About 4-5000 years ago people noted that there were approximately 12 cycles of the moon going from new moon to full moon and back to new moon in a year - the year in which they would plough/sow/harvest - creating a lunar calendar of 12 months of 29½ days (they would start a new month when a new moon was sighted) giving a year of 354 days; this is the calendar Muslims use today which is why the month of fasting Ramadan shifts throughout the year.

To correct for the fact that the tropical year is slightly less than 365¼ days and the year is just under ½ a month short, extra months can be inserted into the calendar to keep the plough/sow/harvest times in the same months; this is the calendar Jews use today.

Some 4000 years ago the Summarians had modified the calendar slightly to have 12 months of 30 days each which gives a year of 360 days. This number 360 is very nice as it has 24 factors (unlike 354 which only has 8 and 365 which only has 4), but whether that is the reason it was chosen is not known.

The Summarians possibly divided the sky up into 12 sections (12 is a factor of 360), one for each month of their year, as a calendar so that they could say when a certain group of stars appeared in a certain place it was time for sowing, etc.

They possibly divided the daylight up into 12 hours - matching 1 hour for each of the months.

The Babylonians later refined the Summarian system to divide the day up into 24 hours (24 is also a factor of 360).

Both the Summarians and Babylonians numerology had favour for 6 and 60 (possibly due to the number of factors each has relative to the numbers around them) and both 12 and 24 are multiples of 6 as well as both being factors of 360.

Passed down from the Babylonians is how we measure time: we use sexagesimal (base 60) numbers to count the number of seconds since midnight. As each digit of a sexagesimal number has a (decimal) value of 0-59 trying to create 50 new symbols for 10-59 is difficult, so we use a colon to separate the digits written in decimal instead. For example the time 7:30:15 (fifteen seconds past half past 7 in the morning) is a sexagesmial number with decimal (base 10) value 7 × 60^2 + 30 × 60 + 75 = 27015 which is the number of seconds from midnight to 7:30:15.

Our Zodiac* is an assignment of a section of the sky based on the name of a constellation (which came from the Greeks looking at the sky and imagining a character from their mythology by joining up the stars like a dot-to-dot, and probably using the so named constellations as a picture book when retelling their mythological tales) in that section. Again, this provides a calendar to identify when to do things (naming the optical illusions of aligned stars makes it easier to pass on the wisdom of when to plant, harvest, etc).

* Astrology mixes the Greek mythologically named constellations with the Roman mythologically named planets.