SECONDS
What is a second?:A "second" is a count of oscillations of a chosen physical reference. Different references give different ratios — but every system can be related back to the SI second, defined in 1967 as 9,192,631,770 cycles of the Cs-133 hyperfine transition.
The atom of all temporal measurement. Every clock — from a wristwatch to an optical lattice — is just a count of one specific oscillation. Below, every second TIME CORE tracks, ticking live since the Unix epoch (1970-01-01 UTC).
Earth's rotation is not perfectly steady. The IERS (International Earth Rotation Service) publishes the daily "length of day" excess in milliseconds — how much longer or shorter the day was than 86,400 SI seconds.
Today's natural second = 1 + (LOD ms ÷ 1000 ÷ 86400). It shifts every day. Source: IERS finals.daily.iau2000.txt.
The international base unit of time, defined since 1967 as 9,192,631,770 cycles of the caesium-133 hyperfine transition.
Oscillator: 9.1926e+9 Hz
Ticks per second: 9.19e+9
1/86400 of the actual current mean solar day. Earth's rotation slows ~+1 ms per day vs. 86,400 SI s — so today's natural second is fractionally longer than the SI second.
10,000 oscillations of a 32,768 Hz watch crystal — the fundamental tick of every consumer computer and wristwatch.
Oscillator: 3.2768e+4 Hz
Ticks per second: 1.00e+4
10,000,000,000 cycles of the Cs-133 transition — one round 10¹⁰-tick beat of the standard atomic clock.
Oscillator: 9.1926e+9 Hz
Ticks per second: 1.00e+10
10¹⁵ cycles of the Yb+ E3 optical octupole transition (642.12 THz) — current frontier of atomic-time precision.
Oscillator: 6.4212e+14 Hz
Ticks per second: 1.00e+15
10¹⁵ cycles of the Al+ optical clock transition (1.121 PHz) — the most stable and accurate optical reference demonstrated to date.
Oscillator: 1.1210e+15 Hz
Ticks per second: 1.00e+15
1/86400 of one Martian solar day (sol = 88,775.244 SI s) — the natural pulse of Coordinated Mars Time.
1/(20 × 64 × 64) of the current Selene day. The Selene Calendar divides every Moon Month into 32 unequal day-segments (between phase boundaries); each Selene day = 20 hours × 64 minutes × 64 seconds = 81,920 Selene seconds. The exact length shifts every Selene day with the actual lunar cycle.
Multiply any duration in SI seconds by 1 / perSI to convert it into the target second-system. Example: 1 SI s ÷ 0.30517578 = 3.2768 Quartz seconds.
| System | Symbol | SI s per 1 | Per 1 SI s | Oscillator (Hz) |
|---|---|---|---|---|
| SI Second | s | 1.000000000 | 1.0000000 | 9.1926e+9 |
| Today's Natural Second | s⊕ | 1.00000001 | 0.99999999 | — |
| Quartz Second | s_Q | 0.30517578 | 3.2768000 | 3.2768e+4 |
| Cesium Second | s_Cs | 1.08782776 | 0.91926318 | 9.1926e+9 |
| Ytterbium Second | s_Yb | 1.55733768 | 0.64212150 | 6.4212e+14 |
| Aluminum-Ion Second | s_Al | 0.89204841 | 1.1210154 | 1.1210e+15 |
| Mars Second | s_♂ | 1.02749125 | 0.97324430 | — |
| Selene Second | s_☾ | 0.84938818 | 1.1773180 | — |