What is a Second? - Definition & Explanation

[Epsillon]

As the title says what exactly is the defination of a second?

I am very curios about this.

 

[Sutitan]

the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom

taken from wikipedia. but I remember learning it in physics.

Oh, and its the unit of time...

 

[Epsillon]

lol why is it that?

 

[Sutitan]

Well, I guess cause its something consistent that we can measure. They want something that is universally constant in nature.

Its the same with a meter, being defined by distance traveled by light in absolute vacuum in 1⁄299,792,458 of a second.

 

[Epsillon]

But before could they measure the time it took for the radiation or the speed of light?

 

[Sutitan]

Well, the first semi-accurate measurement of time came from pendulums. they had second pendumlums and what not. They also had mechanical clocks which showed seconds and minutes and hours like modern clocks. I doubt they were, but they could have beared a resemblance to modern day grandfather clocks. they based there days off of the ascension of stars.

you can read in depth about it here:
http://en.wikipedia.org/wiki/Second#History

 

[Epsillon]

Thanks :) Interesting article.

 

[Borek]

And the one that you could easily check by yourself before asking...