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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 1044 s The duration light takes to travel one Planck length. Theorized to be the smallest duration measurement that will ever be possible, roughly 1043 seconds.
Yoctosecond 1024 s  
Jiffy varies

in quantum physics, the duration light takes to travel one Fermi(1015m, about the size of a nucleon) in a vacuum: about 3 × 1024s.

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 1021 s  
Attosecond 1018 s Shortest duration now measurable
Femtosecond 1015 s pulse duration on fastest lasers
Picosecond 1012 s  
Nanosecond 10s duration for molecules to fluoresce
Shake 10s 10 nanoseconds. Also a casual term for a short duration.
Microsecond 10s  
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.