Time Scales
UTC · TAI · GPS · TT · UT1 · Unix
The world runs on at least six different definitions of "now". Each scale answers a different question — Earth rotation, atomic oscillation, satellite navigation, planetary ephemerides — and they drift apart at predictable rates. TIME CORE shows them live, side by side.
UTC
reference
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TAI
+10 s (28 leap seconds since 1972)
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GPS
+-9 s vs UTC (TAI − 19)
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TT (Terrestrial)
+42.184 s (TAI + 32.184)
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UT1 (Earth rotation)
from IERS Bulletin A (approx)
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Unix
POSIX seconds since 1970-01-01 UTC (no leap)
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Leap Second Ledger
TAI − UTC since 1972
| Effective UTC Date | TAI − UTC | GPS − UTC |
|---|---|---|
| 2017-01-01 | +37 s | +18 s |
| 2015-07-01 | +36 s | +17 s |
| 2012-07-01 | +35 s | +16 s |
| 2009-01-01 | +34 s | +15 s |
| 2006-01-01 | +33 s | +14 s |
| 1999-01-01 | +32 s | +13 s |
| 1997-07-01 | +31 s | +12 s |
| 1996-01-01 | +30 s | +11 s |
| 1994-07-01 | +29 s | +10 s |
| 1993-07-01 | +28 s | +9 s |
| 1992-07-01 | +27 s | +8 s |
| 1991-01-01 | +26 s | +7 s |
| 1990-01-01 | +25 s | +6 s |
| 1988-01-01 | +24 s | +5 s |
| 1985-07-01 | +23 s | +4 s |
| 1983-07-01 | +22 s | +3 s |
| 1982-07-01 | +21 s | +2 s |
| 1981-07-01 | +20 s | +1 s |
| 1980-01-01 | +19 s | +0 s |
| 1979-01-01 | +18 s | +-1 s |
| 1978-01-01 | +17 s | +-2 s |
| 1977-01-01 | +16 s | +-3 s |
| 1976-01-01 | +15 s | +-4 s |
| 1975-01-01 | +14 s | +-5 s |
| 1974-01-01 | +13 s | +-6 s |
| 1973-01-01 | +12 s | +-7 s |
| 1972-07-01 | +11 s | +-8 s |
| 1972-01-01 | +10 s | +-9 s |
Source: IERS Bulletin C · No leap second has been inserted since 2017-01-01. The CGPM voted in 2022 to abolish leap seconds by 2035.