| Name of unit | Symbol | Definition | Relation to SI units |
|---|
| Atomic unit of time | au | ≡
a0/(
α ·
c ) | ≈
6983241888425400000♠2.418
884254×10
−17 s |
| Callippic cycle | | ≡ 441 mo (hollow) + 499 mo (full) = 76 a of 365.25 d | =
7009239673600000000♠2.396
736 Gsor
7009239837760000000♠2.398
3776 Gs |
| Century | c | ≡ 100 years (100 a) | =
7009315569520000000♠3.155
6952 Gs |
| Day | d | = 24 h =
7003144000000000000♠1440min | =
7004864000000000000♠86.4 ks |
| Day (sidereal) | d | ≡ Time needed for the Earth to rotate once around its axis, determined from successive transits of a very distant astronomical object across an observer's meridian (
International Celestial Reference Frame) | ≈
7004861641000000000♠86.1641 ks |
| Decade | dec | ≡ 10 years (10 a) | =
7008315569520000000♠315.569
520 Ms |
| Fortnight | fn | ≡ 2 wk | =
7006120960000000000♠1.2096 Ms |
| Helek | | ≡
1⁄
7003108000000000000♠1080h | = 3.
3s |
| Hipparchic cycle | | ≡ 4 Callippic cycles - 1 d | =
7009959342400000000♠9.593
424 Gs |
| Hour | h | ≡ 60 min | =
7003360000000000000♠3.6 ks |
| Jiffy | j | ≡
1⁄
60s | = 16.
6ms |
| Jiffy (alternative) | ja | ≡
1⁄
100s | = 10 ms |
| Ke(quarter of an hour) | | ≡
1⁄
4h =
1⁄
96d = 15 min | = 900 s |
| Ke (traditional) | | ≡
1⁄
100d = 14.4 min | = 864 s |
| Lustre; Lustrum | | ≡ 5 a of 365 d
| =
7008157680000000000♠157.68 Ms |
| Metonic cycle; enneadecaeteris | | ≡ 110 mo (hollow) + 125 mo (full) = 6940 d ≈ 19 a | =
7008599616000000000♠599.616 Ms |
| Millennium | | ≡
7003100000000000000♠1000years (
7010315576000000000♠1000 a) | =
7010315569520000000♠31.556
952 Gs |
| Milliday | md | ≡
1⁄
7003100000000000000♠1000d | = 86.4 s |
| Minute | min | ≡ 60 s, due to
leap secondssometimes 59 s or 61 s, | = 60 s
|
| Moment | | ≡ 90 s | = 90 s |
| Month(full) | mo | ≡ 30 d
| =
7006259200000000000♠2.592
×10
6 s |
| Month (Greg. av.) | mo | =
7006262974600000000♠30.436
875 d | ≈
7006262970000000000♠2.6297 Ms |
| Month (hollow) | mo | ≡ 29 d
| =
7006250560000000000♠2.5056 Ms |
| Month (
synodic) | mo | Cycle time of moon phases ≈
7006255144288960000♠29.530
589 d(average) | ≈
7006255100000000000♠2.551 Ms |
| Octaeteris | | = 48 mo (full) + 48 mo (hollow) + 3 mo (full)
= 8 a of 365.25 d = 2922 d | =
7008252460800000000♠252.4608 Ms |
| Planck time | | ≡ (
Gℏ⁄
c5)
1⁄
2 | ≈
6957135121186800000♠1.351
211868×10
−43 s |
| Second | s | Time of
7009919263177000000♠9
192631770periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom at 0 K
(but other seconds are sometimes used in astronomy). Also that time it takes for light to travel a distance of
7008299792458000000♠299
792458metres. | (
SI base unit) |
| Shake | | ≡ 10
−8s | = 10 ns |
| Sigma | | ≡ 10
−6s | = 1 μs |
| Sothic cycle | | ≡
7003146100000000000♠1461a of 365 d | =
7014460740960000000♠460.740
96 Ts |
| Svedberg | S | ≡ 10
−13s | = 100 fs |
| Week | wk | ≡ 7 d = 168 h =
7005604800000000000♠10
080 min | =
7005604800000000000♠604.8 ks |
| Year(common) | a, y,
oryr | 365 d | =
7007315360000000000♠31.536 Ms |
| Year (Gregorian) | a, y,
oryr | = 365.2425 d average, calculated from common years (365 d) plus leap years (366 d) on most years divisible by 4. See
leap yearfor details. | =
7007315569520000000♠31.556
952 Ms |
| Year (Julian) | a, y,
oryr | = 365.25 d average, calculated from common years (365 d) plus one leap year (366 d) every four years | =
7007315576000000000♠31.5576 Ms |
| Year (leap) | a, y,
oryr | 366 d | =
7007316224000000000♠31.6224 Ms |
| Year (mean tropical) | a, y,
oryr | Conceptually, the length of time it takes for the Sun to return to the same position in the cycle of seasons,
[Converter 1]approximately
7002365242190000000♠365.242
19d, each day being
7004864000000000000♠86
400SI seconds
| ≈
7007315569250000000♠31.556
925 Ms |
| Year (sidereal) | a, y,
oryr | ≡ Time taken for Sun to return to the same position with respect to the stars of the celestial sphere, approximately
7007315581497632000♠365.256
363 d | ≈
7007315581497632000♠31.558
1497632 Ms |
Notes:
- Jump up^see
Callippic cyclefor explanation of the differences
- ^
Jump up to:abcThis is based on the average Gregorian year. See above for definition of year lengths.
- ^
Jump up to:abcdefghijklmnopWhere
UTCis observed, the length of this unit may increase or decrease
depending on the number of
leap secondswhich occur during the time interval in question. - Jump up^The length of ancient lustral cycles was not constant; see
Lustrumfor more details
|