Leap Years e Leap Seconds
Por que We Adjust Our Clocks
Learn Sobre Tempo AdjustmentsEarth's orbit doesn't fit neatly into whole days, e its rotation gradually slows. Leap years e leap seconds são o corrections esse keep our calendars aligned com seasons e our clocks synchronized com Earth's actual rotation.
Leap Years Explained
Por que We Need Them
Earth orbits o Sun in aproximadamente 365.2422 days—not exatamente 365. Sem correction, o calendar would drift by sobre 1 day todo 4 years, eventually putting summer months in winter.
O Gregorian Leap Year Rule
- Years divisible by 4 são leap years
- EXCEPT years divisible by 100 são NOT leap years
- EXCEPT years divisible by 400 ARE leap years
Examples
| Year | Divisible by 4? | Divisible by 100? | Divisible by 400? | Leap Year? |
|---|---|---|---|---|
| 2024 | Yes | No | No | Yes |
| 2100 | Yes | Yes | No | No |
| 2000 | Yes | Yes | Yes | Yes |
| 1900 | Yes | Yes | No | No |
Accuracy of o Gregorian Calendar
| Calendar | Average Year Comprimento | Error vs. True Year |
|---|---|---|
| 365-day (no leap) | 365.0000 days | ~1 day todo 4 years |
| Julian (leap todo 4) | 365.2500 days | ~1 day todo 128 years |
| Gregorian | 365.2425 days | ~1 day todo 3,236 years |
| Actual tropical year | 365.2422 days | — |
O Gregorian calendar é preciso enough esse it won't need further correction for millennia.
Leap Seconds Explained
Por que We Need Them
Earth's rotation é gradually slowing (sobre 1.4 milliseconds per century) due to tidal friction. Atomic clocks, no entanto, keep perfect time. Leap seconds reconcile estes:
- Atomic time (TAI) counts perfect seconds
- Universal Tempo (UT1) tracks Earth's actual rotation
- UTC adds leap seconds to stay within 0.9 seconds of UT1
Como They're Added
Quando needed, a leap segundo é inserted at 23:59:59 UTC on June 30 ou December 31, creating a moment quando clocks show 23:59:60 before rolling to 00:00:00.
Leap Seconds História
| Period | Leap Seconds Added | Notes |
|---|---|---|
| 1972 | +10 seconds | Initial UTC adjustment |
| 1972-1979 | +9 seconds | Nearly annual additions |
| 1980-1999 | +15 seconds | Regular additions |
| 2000-2016 | +4 seconds | Slowing need |
| 2017-2024 | 0 seconds | None added recently |
| Total (through 2024) | 27 seconds | UTC é 27s behind TAI |
Earth's rotation varies unpredictably; negative leap seconds may eventually be needed.
Born on February 29?
"Leap day babies" (leaplings) têm birthdays esse apenas occur todo 4 years. Legal conventions vary:
- A maioria jurisdictions: Age advances on March 1 in non-leap years
- Alguns contexts: February 28 é usado
- O person tem ainda lived o mesmo number of days as anyone else their age
Famous leaplings: Ja Rule, Tony Robbins, Dinah Shore.
Conclusão
Leap years keep our calendar aligned com Earth's orbit around o Sun, adding a day todo 4 years (com century exceptions). Leap seconds keep atomic clocks aligned com Earth's gradually slowing rotation. While leap years will continue indefinitely, leap seconds são being phased out by 2035 due to o problems they cause for computing systems.