How long is a second in time
- how long is one second
- = 1 s
- how long is one second in a black hole
- how long is one second in the hyperbolic time chamber
How long is a second in seconds
How many milliseconds in a second.
Second
SI unit of time
This article is about the unit of clock time. For other uses, see Second (disambiguation).
The second (symbol: s) is a unit of time, historically defined as 1⁄86400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each (24 × 60 × 60 = 86400).
The current and formal definition in the International System of Units (SI) is more precise:
The second [...] is defined by taking the fixed numerical value of the caesium frequency, ΔνCs, the unperturbed ground-statehyperfine transition frequency of the caesium 133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s−1.[1]
This current definition was adopted in 1967 when it became feasible to define the second based on fundamental properties of nature with caesium clocks.[2] Because the speed of Earth's rotation varies and is slowing ever so slightly, a leap second is added at irregular intervals to civil time[nb 1] to keep clocks in sync with Earth's rotation.