A unit of time or time unit is any particular time intravel, used as a
standard way of measuring or expressing duration. The base unit of
time in the
International System of Units
The duration of 7009919263177000000♠9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.[1] Historically units of time were defined by the movements of astronomical objects.
Sun
These units do not have a consistent relationship with each other and
require intercalation. For example, the year cannot be divided into 12
28day months since 12 times 28 is 336, well short of 365. The lunar
month (as defined by the moon's rotation) is not 28 days but 28.3
days. The year, defined in the
Gregorian calendar
Contents 1 Historical 2 Scientific time units 3 List 4 Units of time interrelated 5 References Historical[edit]
Main article:
History
Horizontal logarithmic scale marked with units of time in the Gregorian calendar Scientific time units[edit] The jiffy is the amount of time light takes to travel one fermi (about
the size of a nucleon) in a vacuum.
Planck time is the time light takes to travel one Planck length.
Theoretically, this is the smallest time measurement that will ever be
possible. Smaller time units have no use in physics as we understand
it today.
The TU (for
Time
Note: The lightyear is not a unit of time, but a unit of length of about 9 trillion kilometres (9,454,254,955,488 kilometres). List[edit] Units of time Unit Length, Duration and Size Notes Planck time unit 5.39 x 10−44 s The amount of time light takes to travel one Planck length. Theoretically, this is the smallest time measurement that will ever be possible.[3] Smaller time units have no use in physics as we understand it today. yoctosecond 10−24 s jiffy (physics) 3 × 10−24s The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum. zeptosecond
10−21 s
Time
attosecond 10−18 s femtosecond 10−15 s Pulse time on fastest lasers. Svedberg
10−13 s
Time
picosecond 10−12 s nanosecond
10−9 s
Time
shake 10−8 s 10 nanoseconds, also a casual term for a short period of time. microsecond 10−6 s Symbol is µs millisecond 0.001 s Shortest time unit used on stopwatches. jiffy (electronics) 1/60s to 1/50s Used to measure the time between alternating power cycles. Also a casual term for a short period of time. second 1 sec SI Base unit. minute 60 seconds moment 1/40th of an hour (90 seconds) Medieval unit of time used by astronomers to compute astronomical movements.[4] ke 14 minutes and 24 seconds Usually calculated as 15 minutes, similar to "quarter" as in "a quarter past six" (6:15). 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 called "sennight". megasecond 1,000,000 seconds About 11.6 days. fortnight 2 weeks 14 days lunar month 27 days 4 hours 48 minutes–29 days 12 hours Various definitions of lunar month exist. month 28–31 days Occasionally calculated as 30 days. quarter and season 3 months semester an 18week division of the academic year[5] Literally "six months", also used in this sense. year 12 months or 365 days common year 365 days 52 weeks and 1 day. tropical year 365 days and 5:48:45.216 hours[6] Average. Gregorian year 365 days and 5:49:12 hours[7] Average. sidereal year 365 days and 6:09:09.7635456 hours leap year 366 days 52 weeks and 2 days. biennium 2 years triennium 3 years quadrennium 4 years olympiad 4 year cycle 48 months, 1,461 days, 35,064 hours, 2,103,840 minutes, 126,230,400 seconds. lustrum 5 years decade 10 years indiction 15 year cycle score 20 years gigasecond 1,000,000,000 seconds About 31.7 years. jubilee 50 years century 100 years millennium 1,000 years Also called "kiloannum". terasecond 1 trillion seconds About 31,700 years. Megannum 1,000,000 (106) years Also called "Megayear." About 1,000 millennia (plural of millennium), or 1 million years. petasecond 1015 seconds About 31,700,000 years galactic year Approximately 230 million years[2] The amount of time it takes the Solar System to orbit the center of the Milky Way Galaxy one time. 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. aeon 1,000,000,000 years or an indefinite period of time Also spelled "eon"
Day
exasecond 1018 seconds About 31,700,000,000 years zettasecond 1021 seconds About 31.7 trillion years yottasecond 1024 seconds About 31.7 x 1015 years Units of time interrelated[edit] Flowchart illustrating the major units of time All of the important units of time can be interrelated. The key units are the second, defined in terms of an atomic process; the day, an integral multiple of seconds; and the year, usually 365.25 days. Most of the other units used are multiples or divisions of these three. The graphic also shows the three heavenly bodies whose orbital parameters relate to the units of time. References[edit] ^ "Definitions of the SI base units". The NIST reference on Constants,
Units, and Uncertainty. National Institute of Standards and
Technology. Retrieved 4 March 2016.
^ a b
http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question18.html
NASA  StarChild Question of the
Month
v t e Time Key concepts Past history deep time Present
Future
Futures studies
Far future in religion
Far future in science fiction and popular culture
Timeline
Measurement and standards Chronometry UTC UT TAI Unit of time Planck time Second Minute Hour Day Week Month Season Year Decade Century Millennium Tropical year Sidereal year Samvatsara Measurement systems
Time
Calendars Gregorian Julian Hebrew Islamic Lunar Solar Hijri Mayan Intercalation Leap second Leap year Clocks Horology
History
astrarium atomic quantum marine sundial sundial markup schema watch waterbased Chronology History Astronomical chronology
Big History
Calendar
Religion Mythology Dreamtime
Kāla
Kalachakra
Prophecy
Time
Philosophy of time Aseries and Bseries Btheory of time Causality Duration Endurantism Eternal return Eternalism Event Multiple time dimensions Perdurantism Presentism Static interpretation of time Temporal finitism Temporal parts The Unreality of Time Human experience and use of time Accounting period
Chronemics
Fiscal year
Generation time
Mental chronometry
Music
Procrastination
Punctuality
Temporal database
Term
Time
Specious present Timetracking software
Timeuse research
Timebased currency
Time
Geology Geological time age chron eon epoch era period Geochronology Geological history of Earth Physics Absolute time and space
Arrow of time
Chronon
Coordinate time
Imaginary time
Planck epoch
Planck time
Proper time
Rate
Spacetime
Theory of relativity
Time
gravitational
Time
other subject areas Chronological dating
Chronobiology
Circadian rhythms
Dating methodologies in archaeology
Time
Related topics Carpe diem
Clock
Time
v t e
Time
Chronometry Orders of magnitude Metrology International standards Coordinated Universal Time offset UT
ΔT
DUT1
International Earth Rotation and Reference Systems Service
ISO 311
ISO 8601
International Atomic Time
6hour clock
12hour clock
24hour clock
Barycentric Coordinate Time
Barycentric Dynamical Time
Civil time
Daylight saving time
Geocentric Coordinate Time
International Date Line
Leap second
Solar time
Terrestrial Time
Time
Obsolete standards Ephemeris time Greenwich Mean Time Prime meridian
Time
Absolute time and space
Spacetime
Chronon
Continuous signal
Coordinate time
Cosmological decade
Discrete time and continuous time
Planck time
Proper time
Theory of relativity
Time
Horology Clock
Astrarium
Atomic clock
Complication
History
Calendar Astronomical Dominical letter Epact Equinox Gregorian Hebrew Hindu Intercalation Islamic Julian Leap year Lunar Lunisolar Solar Solstice Tropical year Weekday determination Weekday names Archaeology and geology Chronological dating Geologic time scale International Commission on Stratigraphy Astronomical chronology Galactic year Nuclear timescale Precession Sidereal time Other units of time Flick Shake Jiffy Second Minute Moment Hour Day Week Fortnight Month Year Olympiad Lustrum Decade Century Saeculum Millennium Related topics Chronology Duration music Mental chronometry
Metric time
System time
Time
