Science Questions

Why is a day divided into 24 hours?

Tue, 23rd Feb 2016

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Anthony asked:

Why do we have a 24 hour day cycle, and could we make it metric?


Kat just about found time to ask Stuart this question... Is time infinite?

Stuart - So this is really interesting because itís actually an historical question.  So historians have attributed this division of the day into 24 hours to the ancient egyptians.  And the idea is they had 10 hours for the daytime, 10 hours for the nighttime, plus 2 hours each for the dusk and dawn, and thatís what formed the 24 hour clock.  And thereís an idea that this might have been linked to the number of stars that astronomers were seeing in the night sky at the that time, that maybe there was around 12 stars that occur during different phases of the night.  And thatís what gives us our 24 hour clock.

Kat - But where does the 60 minutes and 60 seconds come from?

Stuart - So that even more interesting.  Itís not from the same place and so this idea of 60, this base 60 system.  When I say base 60, I mean when we start counting from 0 to 59, thatís the number of digits that represent our time.  That kind of goes back to the Babylonians and the idea that they were fascinated with this idea of 60 and weíre not too sure why but historians think, or people have speculated that itís due to the fact that 60 is a very good number for dividing into different fractions. And thatís the way the base 60 minutes and 60 seconds comes from.

Kat - Well would it work if we say had metric time.  Would that be possible or just completely confusing for everyone?

Stuart - So itís important to specify what we mean by metric time.  Our SI unit of time, the base unit that scientist use to measure time is the second and thatís standard.

Kat - You get milliseconds though.  So thatís going from base to into decimal.

Stuart - Yes, so that is already a metric, a decimalised form of time and thatís commonly used throughout the sciences because itís easy to work with; we like counting to ten.  And actually itís a real problem because if you think about how computers work, which are reliant on date and time, how to record that on a computer is a really challenging problem. So a lot of systems, in particular ones that are based on an architecture called Unix, use a specific point thatís the start of time.  They use January 1st, 1970Ö

Chris - 1970.  And thatís what lead to the millennium bug, wasnít it?

Stuart - Itís one of the reasons.  The millennium bug specifically was about what happens when the programmes were being a bit lazy and only recorded the last two digits of the date, like 00 or 01.  But actually, thereís a proposed problem coming up in 2038 which is where, basically, we ran out of space to store the number of second since 1970, which is how computers count time.

Chris - So what will they do about the Unix time stamp problem then when potentially run out of space?  Is there a new solution to surmount that?

Stuart - Yes.  So the problem is down to basically how much space you allocate in the computer to count the number of seconds.  So what Unix time means is that the computer is just counting from zero seconds (1st January, 1970) up to the current time in seconds and that has itís own problems because, actually, the solar year and the solar times are all complicated.  Thereís leap seconds, we need to adjust for the rotation of the earth moving - itís a very complicated issue.  But what you can do, of course, is just redesign your system and if you implement, basically, software updates.  Thatís what you need to do - update your system - very important.


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It possibly derived from dividing the day into 12 parts with a sundial.
Sundials don't work at night, but they mirrored the day pattern at night, for a total of 24 hours.


The French tried, after the French Revolution - they even had decimal weeks. It was later repealed.
More recently, a trendy Swiss watch company also attempted it, but it seems to have faded into obscurity.
See: evan_au, Wed, 10th Feb 2016

They might metricize the day after they get rid of the QWERTY keyboard, but very likely not sooner. Atomic-S, Fri, 12th Feb 2016

I think we will sooner go from decimal to duodecimal number system. chiralSPO, Fri, 12th Feb 2016

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