how is one second calculated?

Answer 1

I'll take a simpler interpretation of the question and say one second is "calculated" to be 1/86400th of a day, where 86400 is the product of 24 hours times 60 minutes/hour times 60 seconds/minute. Problem is that the day (say from local noon to local noon by measuring the sun's highest point in the sky) is not constant throughout the year, so it was decided to use the average day looking over the whole year.
For very precise timings of experiments in the laboratory, one needs a very good pendulum or something else that oscillates or vibrates at a very constant frequency; then you can work back to what fraction of a day or how many seconds something takes.
In modern times cesium atoms provided the constant well defined measurable frequency, and scientists agreed to "define" one second as some number of these oscillations (9,192,631,770). Now when the earth decides to rotate at a different rate, scientists add leap seconds instead of redefining the second every year.
Lately the reliability of the cesium atom has been questioned, and since the speed of light (in vacuum) is defined as a fundamental "constant", the second can indeed be defined as how long it takes light to go some distance (299,792,458 meters), but that seems circular to me because I see a meter defined as how far light goes in 1/299,792,458 of a second.

Answer 2

The second is currently defined as 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. This definition refers to a caesium atom at rest at a temperature of 0 K.

The meter is defined as the distance travelled by light in absolute vacuum in 1/299,792,458 of a second.

These definitions are not circular. Both definitions are arbitrary. The only fundamental quantity here is the speed of light in a vacuum. The meter and second were redefined so that they would have scientifically precise definitions, and their values would be approximately the values we've used for them for years.

Answer 3

Under the International System of Units, the second is currently defined as 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. This definition refers to a caesium atom at rest at a temperature of 0 K.

The international standard symbol for a second is s (see ISO 31-1).

Answer 4

Originally it came from simple ways of dividing up the day. Back then, people hadn't cottoned on to the simplicity of the metric system and everything was divided up oddly. So they split the day into 24 sections,and then split the hours in 60 sections and those minutes into a similar 60 sections.

Because people seemed to love the number 12. I mean, why? Ten is so much easier, but there you have it - that is the brief histoy of the second.

Answer 5

The above definations were valid till the late 1990s...
now 1 second is the interval in which light travels 1/299,727,458 of a metre in vaccuum.

Answer 6

apparently a cesium atom has some sort of frequency
of 9192631770 Hz, so suitable physics equipment can automatically count out seconds and fractions of seconds.