|
|
Why are there 24 hours in a day?Adapted from http://james.lab6.com and several other non-copyrited internet sources + my own interpretations. What do YOU think? The question was asked at our last club meeting by our speaker… He said he’d asked the question at his talks for the last 30 years and never had anyone answer it correctly! I couldn’t stand it and have done a bit of web research. Read on and you’ll be ready for this question the next time! The question seems to be a simple one. It seems easy enough and we take it for granted, but where do our units of time measurement come from? Why does everyone on the earth split the day up into 24 segments? You can easily understand why there are 365 days in a year. There are 365 risings and settings of the sun before the same season returns and the constellations are in exactly the same position in the sky. This was established by many cultures in far flung locations throughout the world. Pretty easy. This has been realized since before recorded history. How many days are in a month? Even the name “month” gives you a hint at the answer to this one. It’s related to the Moon and its visual lunar phases. There are about 29.5 days between new moons. While the orbital period of the Moon is 27.3 days, what was important to ancient cultures was how long it was between the same visual lunar phases. How many months are in a year? If you divide 365 days per year by 29.5 days per lunar cycle, you’ll get an answer that is a bit more than 12. This is why some months have 30 days, some 31, and one has 28 days to keep the calendar aligned with the seasons from year to year. But what about hours? Why 24? Why not 10? Why not 60? Time is not naturally split up into 24 anythings, so the division must be totally artificial. The origin appears to lie with the Sumerians, over 4000 years ago. When they counted things, they used their fingers, but they did it a bit differently than we do today. Take a look at the fingers on your left hand. Using your thumb, point to the first segment on your index finger between your palm and the rest of the finger. You’ll notice that each of your fingers has three distinct segments where your fingers bend, for a total of twelve segments on your left hand (night). You can count another twelve segments for the day on your right hand. Have you ever noticed this? The Sumerians knew that the time from sunrise to sunrise (on average) was divided evenly between night and day, a left hand and a right hand, everything in balance. They called each of these time segments an “hour.” Interestingly, the Sumerians counted by twelves (called ‘base 12’) instead of by tens (base 10) like we commonly do today. Could this odd 24 unit division of a day be the ancient Sumerians' fault? The ancient Babylonians inherited this quaint practice, and presumably added their own ‘base 60’ oriented counting system to divide the hours into 60 minutes, and the minutes into 60 seconds. The Babylonian fascination with the number 60 is interesting in itself. As well as being fond of twelve (3 x 4) the Babylonians actually used a base sixty notation (3 x 4 x 5). There are 360 degrees (3 x 4 x 5 x 6) in a complete revolution and they liked simple geometric series. This explanation boils down to the Sumerian’s 12-segmented hand system being incorporated by the Babylonian’s 60-centric system. Perhaps our 12-segmented hands were a reason for liking base 60 in the first place. In order to track time at night, the Babylonians divided the sky into the 12 signs of the Zodiac, each sign occupying about 30 degrees. The day and night were each 12 hours long, although in many time systems the lengths of these varied between summer and winter. Babylon was near the equator, so they didn't get too confused with this. Each Zodiacal sign ‘lived’ half in darkness and half in light during the course of a year, so they did not need 24 signs of the Zodiac, which was good since this nicely fit with the number of significant constellations already known by the ancients. None of these solve the problem of getting the whole world to use 24 hours. Did Babylonian timekeeping spread naturally across the world in the same way Arabic and Hindu mathematical notation did? Did the Babylonians conquer rival countries, which went on to conquer others, and so on? Sorry for the inconclusive ending... what do you think? Note:Hours did not have a fixed length until the Greeks decided they needed such a system for theoretical calculations. Hipparchus proposed dividing the day equally into 24 hours which came to be known as equinoctial hours (because they are based on 12 hours of daylight and 12 hours of darkness on the days of the Equinoxes). Ordinary people continued to use seasonally varying hours for a long time. Only with the advent of mechanical clocks in Europe in the 14th Century, did the system we use today become common place.
|
|