Units of time

A day is the time period of a full rotation of the Earth with respect to the Sun. On average, this is 24 hours (86,400 seconds). As a day passes at a given location it experiences morning, afternoon, evening, and night. This daily cycle drives circadian rhythms in many organisms, which are vital to many life processes.

A month is a unit of time, used with calendars, that is approximately as long as a natural phase cycle of the Moon; the words month and Moon are cognates. The traditional concept of months arose with the cycle of Moon phases; such lunar months ("lunations") are synodic months and last approximately 29.53 days, making for roughly 12.37 such months in one Earth year. From excavated tally sticks, researchers have deduced that people counted days in relation to the Moon's phases as early as the Paleolithic age. Synodic months, based on the Moon's orbital period with respect to the Earth–Sun line,

A week, in the Western and international context, is a unit of time equal to seven days. It is the standard calendrical period between a day and a month in most parts of the world. There are just over 52 weeks in a year, or on average weeks in a month. The days of the week are often used to set work days, rest days, and holy days. The term "week" may also be used to refer to a sub-section of the week, such as the workweek and weekend. Certain weeks within a year may be designated for a particular purpose, such as Golden Week in China and Japan. More informally, certain groups may advocate awar

thumb|Modern day Indonesian [[Gregorian calendar for a Catholic church]] thumb|British calendar, 1851, gilt bronze and malachite, height: 20.3 cm, [[Metropolitan Museum of Art (New York City)]]

A century is a period of 100 years or 10 decades. Centuries are numbered ordinally in English and many other languages. The word century comes from the Latin centum, meaning one hundred. Century is sometimes abbreviated as c.

A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and polar regions, the seasons are marked by changes in the intensity of sunlight that reaches the Earth's surface, variations of which may cause animals to undergo hibernation or to migrate, and plants to be dormant. Various cultures define the number and nature of seasons based on regional variations, and as such there are a number of both modern and historica

type of year that has 366 days, instead of 365 for a common year

thumb|Midnight to 1 a.m. on a 24-hour clock with a digital face

A minute is a unit of time defined as equal to 60 seconds. It is not a unit in the International System of Units (SI), but is accepted for use with SI. The SI symbol for minutes is min (without a dot). The prime symbol is also sometimes used informally to denote minutes.

A millennium () is a period of one thousand years, one hundred decades, or ten centuries, It is also sometimes called a kiloannum (ka) or kiloyear (ky).

A decade (from , , ) is a period of 10 years. It may also be called a decennium (from , ). Decades may describe any ten-year period, such as those of a person's life, or refer to specific groupings of calendar years.

period of time for the ecliptic longitude of the Sun to increase 360°

time standard

calendar year with 365 days

series of eclipses separated by a saros period

smallest describable unit of time

thumb | 300px |Stadium at ancient Olympia, Greece|Olympia

A yuga, in Hinduism, is generally used to indicate an age of time.

method for reckoning time in China

Cyclic day of Brahma in Hindu cosmology lasting 1,000 Yuga Cycles containing 14 Manvantaras and 15 Sandhyās. It is followed by a night (pralaya) of equal length, forming one 24-hour day of Brahma's 100 360-day years.

unit of a quantity of 1,000,000 years

An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the geological eras defined for the history of Earth.

begins on the New Year's Day of the given calendar system and ends on the day before the following New Year's Day

insertion of a leap day, week, or month into some calendar years to make the calendar follow the seasons or moon phases

units of time based on the Moon

measurement unit for time

solar day: unit of time on Mars

unit in chronostratigraphy

visual illustration of the history of the Universe

East Asian phrase used to wish long life

thumb|Miniature from Menologion of Basil II for September 1

A lūstrum (, plural lūstra) was a term for a five-year period in Ancient Rome.

thumb|Face on the Zimmer tower in [[Lier, Belgium: On the outer ring, the hand points to the golden number, or the number of the current year in the metonic cycle. The inner ring shows the epact, which is the age of the moon on the first of January of the current year.]]

thumb|250px|A laboratory ultracentrifuge.

boundary of a stage on the geologic time scale

thumb|The astronomical basis of the Hindu lunar day

A chronozone or chron is a unit in chronostratigraphy, defined by events such as geomagnetic reversals (magnetozones), or based on the presence of specific fossils (biozone or biochronozone). According to the International Commission on Stratigraphy, the term "chronozone" refers to the rocks formed during a particular time period, while "chron" refers to that time period.

1460 year calendar cycle of ancient Egypt

rotation period of a body relative to the primary object it orbits, e.g. solar day

unique form of time zoning by watch maker Swatch for the connected world

time of day in decimal units

concept of time in Hinduism

A fortnight is a unit of time equal to 14 days (two weeks). The word derives from the Old English term , meaning "" (or "fourteen days", since the Anglo-Saxons counted by nights).

A chronon is a proposed quantum of time, that is, a discrete and indivisible "unit" of time as part of a hypothesis that proposes that time is not continuous. In simple language, a chronon is the smallest, discrete, non-decomposable unit of time.

weekend that is at least three days long

ancient Chinese time unit, 12 double-hour periods

28-year cycle of the Julian calendar

approximate year when a model was produced, different from calendar year of actual production

medieval unit of time; equals 1/40 of a medieval hour, i.e. 1/480 of the time interval between sunrise and sunset

time for the Moon to complete one rotation on its axis

A '''''' (plural ) is a length of time roughly equal to the potential lifetime of a person or, equivalently, the complete renewal of a human population.

The word aeon , also spelled eon (in American and Australian English), originally meant "life", "vital force" or "being", "generation" or "a period of time", though it tended to be translated as "age" in the sense of "ages", "forever", "timeless" or "for eternity". It is a Latin transliteration from the ancient Greek word ('), from the archaic (') meaning "century". In Greek, it literally refers to the timespan of one hundred years. A cognate Latin word '' (cf. ) for "age" is present in words such as eternal, longevity and mediaeval''.

Samvatsara (संवत्सर) is a Sanskrit term for a "year" in Vedic literature such as the Rigveda and other ancient texts. In the medieval era literature, a samvatsara refers to the "Jovian year", that is a year based on the relative position of the planet Jupiter, while the solar year is called varsha. A jovian year is not equal to a solar year based on the relative position of Earth and Sun.

thumb|The Nychthemeron Clock in Snowshill Manor, Gloucestershire, UK Nychthemeron , occasionally nycthemeron or nuchthemeron, is a period of 24 consecutive hours. It is sometimes used, especially in technical literature, to avoid the ambiguity inherent in the term day.

pendulum whose period is precisely two seconds

Cycle of four yuga ages in Hindu cosmology: Satya Yuga, Treta Yuga, Dvapara Yuga and Kali Yuga.

Period when eclipses can occur

measurement of time

Pahar (Bengali পহর, Hindi/Nepali: पहर, Punjabi: ਪੈਹਰ, Urdu: ), which is more commonly pronounced peher () is a traditional unit of time used in India, Pakistan, and Bangladesh. One pahar nominally equals three hours, and there are eight pahars in a day. In India, the measure is primarily used in North India and by Hindi-speaking communities throughout the Deccan in Southern India.