Seconds
The second (symbol: s) is a unit of time derived from the division of the day, first into hours, then into minutes, and lastly into seconds, for a total of 24 × 60 × 60 = 86,400 seconds per day. The definition that is based on 1⁄86400 of a rotation of the earth is still used by the Universal Time 1 (UT1) system.
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-state hyperfine transition frequency of the caesium 133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s−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. As the speed of Earth's rotation varies and is slowing ever so slightly, a leap second is added at irregular intervals to civil time to keep clocks in sync with Earth's rotation.
Drafts
- 2025-11-21T00:00:00.000000Z
Seconds
- 2023-05-12T00:00:00.000000Z
Landers
- 2022-04-01T00:00:00.000000Z
Hutchy
- 2023-03-24T00:00:00.000000Z
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