## Units of time

Unit | Length, Duration and Size | Facts |

Instant | varies | Loosely speaking, zero time (colloquially the term may be used in other ways) |

Planck time unit | 5.39 x 10−44 s | The duration light takes to travel one Planck length. Theorized to be the smallest duration measurement that will ever be possible, roughly 10−43 seconds. |

Yoctosecond | 10−24 s | |

Jiffy | varies |
in quantum physics, the duration light takes to travel one Fermi(10−15m, about the size of a nucleon) in a vacuum: about 3 × 10−24s. In electronics, the duration for one alternating current power cycle (1/60 or 1/50 of a second). Also, an informal term for any unspecified short duration. |

Zeptosecond | 10−21 s | |

Attosecond | 10−18 s | Shortest duration now measurable |

Femtosecond | 10−15 s | pulse duration on fastest lasers |

Picosecond | 10−12 s | |

Nanosecond | 10−9 s | duration for molecules to fluoresce |

Shake | 10−8 s | 10 nanoseconds. Also a casual term for a short duration. |

Microsecond | 10−6 s | |

Millisecond | 0.001 s | shortest duration unit used on stopwatches |

Centisecond | 0.01 s | used on some stopwatches |

Decisecond | 0.1 s | used on some stopwatches |

Jiffy(electronics) | ~1/50s to 1/60s | Used to measure the duration between alternating power cycles. Also a casual term for a short duration |

Second | 1 sec | SIbase unit |

Decasecond | 10 seconds | |

Minute | 60 seconds | |

Moment(historical) | 1/40th of an hour | Used by Medieval Western European computists. |

Hectosecond | 100 seconds | 1 minute and 40 seconds |

Ke | 864 seconds | traditional Chinese unit of decimal time duration, usually 1/100 of a day. 14 minutes and 24 seconds. (Nearly 1/4 of an hour.) |

Kilosecond | 1,000 seconds | 16 minutes and 40 seconds |

Hour | 60 minutes | |

Day | 24 hours | longest unit used on stopwatches and countdowns |

Week | 7 days | Also calledsennight |

Megasecond | 1,000,000 seconds | About 11.6 days |

Fortnight | 14 days | 2 weeks (more common in Great Britain) |

Lunar month | 27.2–29.5 days | Various definitions of lunar month exist. |

Month | 28–31 days | Often 30 days for financial and other calculations. |

Quarter and season | 3 months | The duration of any of the four calendar seasons; winter, spring, summer and autumn. |

Year | 12 months | |

Common year | 365 days | 52 weeks + 1 day |

Tropical year | 365.24219 days | average |

Gregorian year | 365.2425 days | average |

Julian year | 365.25 days | |

Sidereal year | 365.256363004 days | |

Leap year | 366 days | 52 weeks + 2 days |

Biennium | 2 years | A unit of time duration commonly used by legislatures |

Triennium | 3 years | |

Olympiad | 4 year cycle | |

Lustrum | 5 years | |

Decade | 10 years | |

Indiction | 15 year cycle | |

Generation | varies | about 17-35 years for humans |

Gigasecond | 1,000,000,000 seconds | About 31.7 years |

Jubilee | 50 years | |

Century | 100 years | |

Millennium | 1,000 years | also called "kiloannum" |

Terasecond | 1012 seconds | About 31,700 years |

Megaannum | 1,000,000 years | 1 million years |

Age | varies | on the geological timescale, some millions of years |

Epoch | varies | on the geological timescale, tens of millions of years |

Petasecond | 1015 seconds | About 31.7 million years |

Era | varies | on the geological timescale, several hundred millions of years |

Galactic year | Approximately 230 million years | The duration it takes the Sun to orbit the centre of the Milky Way galaxy once. |

Eon | varies | on the geological timescale, 500 million years or more.Also "an indefinite and very long period of time". |

Gigaannum | 1,000,000,000 years | 109 years |

Exasecond | 1018 seconds | roughly 31.7 x 109 years, more than twice the age of the universe (on current estimates) |

Zettasecond | 1021 seconds | About 31.7 x 1012 years |

Yottasecond | 1024 seconds | About 31.7 x 1015 years |

Cosmological decade | varies | 10 times the length of the previous cosmological decade, with CÐ 1 beginning either 10 seconds or 10 years after the Big Bang, depending on the definition. |