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Seeing Time

In an educational (maybe) feature of this month’s eDipole, there was a reference to what is probably thought by readers as being a random, unscientific reference to a unit of time—the jiffy. This opened the doors to the eDipole research department. In a reflection of the once, computer-world thinking, there was found a Flow Chart.

This visual documentation provides a partial overview of the units of time.

How many eDipole readers remember your work, and possibly your life being either governed or guided by the helpful visual, activity-defining concept of a Flow Chart?

Many years ago, the eDipole provided a feature sharing the history of navigation and its dependence upon a newly created method of maintaining a previously unnecessary accuracy of time. Since this historic refinement of time keeping, there has been created new methods and measurements of time.

Units of measurement for time have historically been based on the movement of the Sun (as seen from Earth). Shorter intervals were measured by physiological concepts such as drawing breath, winking or the pulse.

Units of time that are expressed in numbers of years include the lustrum (five years) and the Olympiad (four years). The month could be divided into half-months or fortnights, and quarters or weeks.

Longer periods have been expressed in lifetimes or generations (saecula,aion), subdivisions of the solar day in hours. In the Ancient Egyptian calendar, the Sothic cycle was a period of 1,461 years of 365 days. The Medieval (Pauranic) Hindu cosmology is identified for its introducing names for fabulously long time periods, such as kalpa (4.32 billion years).

In classical antiquity, the hour divided the daylight period into 12 equal parts. Because of this varying foundation of the identities of an hour, the “time” of an hour has varied over the course of a year. In classical China, the () was a unit of decimal time. This Asian time divided a day into 100 equal intervals of 14.4 minutes. Joining oriental time of the ke, there were double hours (shíchen) also known as watches. Because one cannot divide 12 double hours into 100 ke evenly, each kewas subdivided into 60 fēn ().

Time concepts somewhat familiar today are traced back to medieval history. The introduction of the minute (minuta; ′) as the 60th part of an hour, the second (seccunda; ′′) as the 60th part of a minute, and the third (tertia; ′′′) as the 60th part of the second dates began in this period of history. They were used by Al-Biruni around AD 1000, and by Roger Bacon in the 13th century. Bacon further subdivided the tertia into a quarta or fourth (′′′′).

Moving to today’s subcontinent, Hindu chronology divides the civil day (daylight hours) into vipalas, palas and ghatikas. Additionally, a tithi is the 30th part of the synodic month.

Another currently familiar time concept with early historical roots, the 14th century was the introduction of the division of the solar day into 24 hours of equal length. This concept had its origin as being the length of a classical hour at equinox used regardless of daylight hours. This became a reality thanks to the development of the first mechanical clocks.

Today, the fundamental unit of time suggested by the International System of Unitsis. Since 1967, the second has been defined by the International Atomic Time standard. It is based on the radiation emitted by a Caesium-133 atom in the ground state. Its definition was calibrated so 86,400 seconds corresponded to a solar day. 31,557,600 (86,400 × 365.25) seconds are a Julian year. This new time standard has the year exceeding the true length of a solar year by about 21 ppm.

Based on the second as the base unit of time, the following time units are currently in use:

minute (1 min = 60 sec)

hour (1 hr = 60 min = 3.6 ks)

Julian day (1 d = 24 hr = 86.4 ks)

week (7 d = 604.8 ks)

Julian year (1 a = 365.25 d = 31.5576 Ms)

decade (10 years/annum)

century (100 annum = 3.15576 Gs)

millennium (1 ka = 31.5576 Gs)

Whether some people have too much time on their hands or they are looking for fame in an usual way, there have been many attempts at defining and controlling the valuable concepts of time. One system had ten days per week, a multiple of ten days in a month, or ten months per year.

Others have been offered. Hexadecimal time divided the Julian day into 16 hexadecimal hours of 1hr 30 min each, or 65,536 hexadecimal seconds (1 hexsec ≈ 1.32 s).

The Planck time (tP), was one that is associated in quantum mechanics is a natural unit of time. In this concept of time, it is the shortest possible interval that can be meaningfully considered. The tP equals about 5.4 × 10−44 s.

The following time definitions, while surely used by a few “experts in time” may be kept for future-nerd discussions or stored by dedicated cross puzzle experts.

Anyone who may have the time need time for learning more about time may be interested in this exhaustive collection of the units of time.

Units of time

Length, Duration and Size



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. Smaller time units have no use in physics as we understand it today.
yoctosecond 10−24 s
jiffy (physics) 3 × 10−24 s The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.
zeptosecond 10−21 s
attosecond 10−18 s shortest time now measurable
femtosecond 10−15 s pulse time on fastest lasers
Svedberg 10−13 s time unit used for sedimentation rates (usually of proteins)
picosecond 10−12 s
nanosecond 10−9 s time for molecules to fluoresce
shake 10−8 s 10 nanoseconds Also a casual term for a short period of time
microsecond 10−6 s
fourth 1/3,600 second medieval unit of time
millisecond 0.001 s shortest time unit used on stopwatches
centisecond 0.01 s used on some stopwatches
third 1/60 s medieval unit of time
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
decisecond 0.1 s used on some stopwatches
second 1 sec SI base unit
dekasecond 10 seconds
minute 60 seconds
moment 1/40th of an hour (~90 seconds) medieval unit of time used by astronomers to compute astronomical movements.[1]
hectosecond 100 seconds 1 minute and 40 seconds
ke 14 minutes and 24 seconds
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 may not be common
lunar month 27 Days 4 hours 48 minutes–29 days 12 hours Various definitions of lunar month exist.
month 28–31 days
quarter and season 3 months
year 12 months or 365 days
common year 365 days 52 weeks + 1 day
tropical year 365 days 5:48:45.216 hours[2] average
Gregorian year 365 days 5:49:12 hours[3] average
sidereal year 365 days 6:09:09.7635456 hours
leap year 366 days 52 weeks + 2 days
biennium 2 years A unit of time commonly used by legislatures
triennium 3 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 “four score and seven years..” = 87 years
generation 17–35 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
age and megaannum 1,000,000 years
epoch 10,000,000 years
petasecond 1 quadrillion seconds About 3.17 epoches
era 100,000,000 years
galactic year Approximately 2.3 eras[4] The amount of time it takes the Solar System to orbit the center of the Milky Way Galaxy one time.
eon 500,000,000 years Also “An indefinite and very long period of time”
gigaannum 1,000,000,000 years
exasecond 1 quintillion seconds roughly 31.7 billion years, more than twice the age of the universe on current estimates
zettasecond 1 sextillion seconds About 31.7 trillion years
yottasecond 1 septillion seconds About 31.7 quadrillion 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.


Do any eDipole readers know of a person who has committed all of these terms to memory? Could it be that person indeed has too much time on his or her hands?

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