# Why does a second last… well… a second?

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Who, how and when decided to count to a second and was like “Yup. This is it. This is a second. This is how long a second is. Everybody on Earth will universally agree that this is how long a second is and use it regardless of culture, origin, intelligence or beliefs”?

In: 1035

Dividing an hour into 60 parts was pretty common in the ancient world, because 60 is a number that divides evenly into many fractions – 1/3, 1/4, 1/2, 1/6. In fact this sexagesimal type of math was pretty common in the ancient world for this reason. Further dividing the minute into 60 seconds is just a logical progression of that. However, people in the pre-modern world would have used relative hours – that is, they counted twelve hours between sunrise and sunset and evenly divided them. This meant that hours were shorter in the winter and longer in the summer, so minutes and seconds would be longer and shorter as well.

It wasn’t until mechanical clocks that the period of the second became standardized as 1/60 of 1/60 of an hour (or 1/24 of the solar day).

The important question is … how long does a first last if the second lasts 1s?

Imagine you have to take the train at 10 am. But if your clock says “10 am” at a different moment than the clock at the train station, you might miss the train.

This was how it used to be. People were late all the time, because my clock did give a different time than your clock.

Then, some very smart people in Paris thought it would be smart to make the time the same for everybody. And decided how long a second lasts.

Now people don’t come too late anymore.

[https://en.wikipedia.org/wiki/Metric_time](https://en.wikipedia.org/wiki/Metric_time)

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*BTW I am not making this up, and it was worse than you might imagine: every city had it’s own “random” timezone, without much system like with the time zones we have now, it was pure chaos. You needed special tables to determine the time in the next city. It did not matter much until dirigibles and trains came along, hence I use trains as example.

Day split into 24h, one hour split into 60 minutes, one minute split into 60 seconds.

12 was a nice number.
60 was a nice number.

then someone thought to take some atom constant to define one second exactly the same for everyone and for eternity.

Go back far enough and an hour wasn’t a consistent length. Romans divided daytime into 12 hours, so a winter hour was shorter than a summer one.