A component of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects.

The SI unit of Time

The SI unit of time is the second and is the duration of 9192631770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of a caesium 133 atom.

60 seconds = 1 minute 60 minutes= 1 hour
1 calendar year=31.536x106 seconds 1 sidereal year=31.55815x106 seconds
1 tropical year=31.55693x106 seconds 1 sidereal second=0.9972696 s
1 decennium=10 years

Civil Year

A year as measured by the conventional calendar, equal to 365 days in most years but 366 days in a leap year.

Famous Quotes

"Put your hand on a hot stove for a minute, and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute. THAT′S relativity." Albert Einstein


Abbreviation for billion years with the a taken from the French word for year, année, or the Latin word, annum.


Abbreviation for million years with the a taken from the French word for year, année, or the Latin word, annum.

Tropical Year

Also called the mean solar year or nautical year, is dependent on the seasons. It is the interval between two consecutive returns of the sun to the vernal equinox. In 1900, that took 365 days, 5 hours, 48 minutes, and 46 seconds, and it is decreasing at the rate of 0.53 second per century.

See also: Anno Domini, Atomic Clock, Atomus, bell, Clock, Common Era, Coordinated Universal Time, Day, Greenwich Mean Time, Hour, Julian Day, Local Time, Lunar Month, Minute, Proper Time, Second, Sexagesimal, SI Units, Spacetime, Time Zones, Twenty Four Hour Clock, watch, Week.

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Greenwich Mean Time Greenwich Mean Time is international time, the basis of the world time clock.