A measurement of time

On an everyday basis we look at the clock(-maybe not the best way to start a post to get you interested but nothing else comes out of my mind at a very late hour),we look at our watches and always ask "What time is it?" as we always find ourselves in between activities.With such rush we hardly ever ask ourselves "what's the deal with time?" or even "what is time?" to be more  exact.And the thing is,it's quite hard to define the term.It's soo familiar to us in soo many ways as it practically dictates our lives yet when we try answering questions about it,most of what we know or we think we do, seems very close to a blur.

It looks like a much easier question to answer is
"how do we measure time?".It makes everything lighter in terms of understanding,for if we take into account the past,present and future and consider more than 3 dimensions(in physics a dimension has the number of coordinated that are needed to specify a point within it) it gets more and more complicated.

Before getting-or at least trying-into more complex theories(which I will attempt in a future post-consider this Part I),how we measure time seems a good point to start from-the instrument and the science.

The clock is an instrument that indicates time-the moment of a day.The first clock was and still is Earth itself,as it rotates, on its axis and around the Sun(yearly).How is this clock used and how efficient?Nowadays we mostly use electronic clocks which we could say are accurate enough,but we didn't do so in the past.If we go back in time(as we cannot help but use the word again) we look at days measured with the rise and the setting of the Sun.The clock is basically one of our oldest inventions for measuring intervals of time:day,lunar month,year.A good example that operates with this Earth clock and the Sun is the sundial -which tells the time-moment of the day by the position of the Sun-reflecting the process of rotation of our planet around it.The sundial uses shadows-by "displaying" the shadows on a flat surface(usually) with different markings for hours(in general they had morning and afternoon).This kind of clock was widely used in ancient times with reasonable accuracy.It's kind of obvious that it has a pretty big flaw for us,as of right now as it depends on solar light,working in parallel with it- 

night time: a completely different story.Thus ,this encouraged the usage of other techniques.

What about a water clock,then?Old and also known as clepsydrae. Given the antiquity ,their first "appearance" is not known but if we look at certain areas of the world ,like Babylon and Egypt ,one of the simplest forms of the water clock existed around the 16th century BC.This kind of clock would allow people to read the time during night time.There are now many designs of water clocks,the Egyptian one resembling a cone upside down,with a whole in the middle allowing water to flow out of it.The body would be marked so that as water was flowing out you could see when an hour had passed.There's a simple description of this tool on this site.

In general,it looks like the older we get the accuracy of time measurement improves.From astrological to pendulum and today's electric clocks,everything evolves and changes.

Then we go on to temporal measurement or chronometry.If the clock equals the device then chronometry equals the science of the measurement of time(it is not the same with chronology-that is another science).Time measurement devices I talked about above are just 2 examples from quite the range-a great variety has been invented.The study of these devices is known as horology(yes,there's a name for everything...I believe...).When we talk about time we "divide" moments.The second-symbol: s -is the base unit of time in the International System of Units.It is the second division of the hour by 60(the first being the minute):

1 minute...60 seconds

1 hour.......60 minutes...60*60 seconds

(1 hour is divided into 60 minutes so into 3600 seconds)

There have been several definitions.Until the 1960s it was defined as 1/86400 of a mean solar day(which still applies in some cases/contexts).

A solar day is the unit of solar time-that deals with the passage of time based on the Sun's motion across the sky:     ->used for sundials:sundial time

       ->mean solar time:clock time

Then,for about 7 years ,(it was defined)in terms of the period of the Earth's orbit around the Sun and now it is precisely defined in atomic terms.

But what is time?

-dun dun dun dunnnnnn-

(I had to type that....)

Cristina