It seems like everything with our calendar is based around 24hr days and the number of 24hr days to revolve around the sun. But a 24hr day can be broken down to 1,440 minutes and in turn 86,400 seconds. How did we (humans) calibrate the second so that exactly 86,400 would be 1 rotation of the earth to the point where we never need something like a “leap second” like we have with leap years?
In: Planetary Science
> to the point where we never need something like a “leap second” like we have with leap years?
We do have [leap seconds](https://en.wikipedia.org/wiki/Leap_second).
The most precise definition of a second comes from [atomic clocks](https://en.wikipedia.org/wiki/Atomic_clock) which use the frequency of light emitted by atoms as a baseline. Whenever an electron within an atom undergoes a particular change in its energy state, it emits a very particular frequency of light.
Atomic clocks don’t line up with solar time, which is why leap seconds do exist.
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