system
Given the following post, respond as if you're commenting on Reddit:
human
The "second" is 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 cesium 133 atom... How did we discover this?

How was it defined before this discovery, and what led to our exact definition of the length of time that we know as a "second"? And as a bonus, how on earth do we count those oscillations?
gpt
A day is the time span between two sun rises. An hour is a twentyfourth of a day. A minute is a sixtieth of an hour. A second is a sixtieth of a minute. That's how it was measured before. Obviously this is not exactly an accurate way of measuring time (it starts with each day being slightly shorter/longer than the one before), but it used to be enough.