Units Of Time

Unit	Size	Notes
yoctosecond	10−24 s
zeptosecond	10−21 s
attosecond	10−18 s	shortest time uncertainty in present measurements
femtosecond	10−15 s	pulse time of ultrafast lasers (100 as = 0.1 fs)
picosecond	10−12 s
nanosecond	10−9 s	time for molecules to fluoresce
microsecond	10−6 s
millisecond	0.001 s
second	1 s	base unit
minute	60 seconds
hour	60 minutes
day	24 hours
week	7 days	Also called sennight
fortnight	14 days	2 weeks
lunar month	27.2–29.5 days	Various definitions exist.
month	28–31 days
quarter	3 months
year	12 months
common year	365 days	52 weeks + 1 day
leap year	366 days	52 weeks + 2 days
tropical year	365.24219 days	average
Gregorian year	365.2425 days	average
Olympiad	4 year cycle
lustrum	5 years	Also called pentad
decade	10 years
Indiction	15 year cycle
generation	17–35 years	approximate
jubilee (Biblical)	50 years
century	100 years
millennium	1,000 years
exasecond	1018 s	roughly 32 billion years, more than twice the age of the universe on current estimates
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.

Time

Time is a dimension in which events can be ordered from the past through the present into the future,and also the measure of durations of events and the intervals between them. Time has long been a major subject of study in religion, philosophy, and science, but defining it in a manner applicable to all fields without circularity has consistently eluded scholars. Nevertheless, diverse fields such as business, industry, sports, the sciences, music, dance, and the live theater all incorporate some notion of time into their respective measuring systems.Some simple, relatively uncontroversial definitions of time include "time is what clocks measure" and "time is what keeps everything from happening at once".

Clocks

Clocks

Clocks

Clocks

The First Tick

The first mechanical clocks had a weight that would slowly lower, moving gears which moved a hand which showed the hour. They could only be build in tall towers because the weights needed to fall a great distance or else the clocks would only work for a short amount of time. People were amazed that these clocks were only off about 2 hours a day. Think if our clocks today were off by that much? If we were 2 hours late for school, we could blame it on the clock. While these clocks were inaccurate long ago, some of them were created with such care that they still work today. In Normandy, France, a big clock exists that was built in 1389. In Salisbury, England you can see the oldest clock in the world, built in 1386. Today, cuckoo clocks are still built using a weight-dropping mechanism.