Calendars

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,

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 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

first day of the year according to some calendar (e.g., January 1 in the Julian and Gregorian calendar)

A solstice is the time when the Sun reaches its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around 20–22 June and 20–22 December. In many countries, the seasons of the year are defined by reference to the solstices and the equinoxes.

type of calendar

particular day represented within a calendar system

calendar based on the solar time of the tropical year with months related to the regular cycle of the Moon's phases

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

In astronomy and celestial navigation, an ephemeris (; ; , ) is a book with tables that gives the trajectory of naturally occurring astronomical objects and artificial satellites in the sky, i.e., the position (and possibly velocity) over time. Historically, positions were given as printed tables of values, given at regular intervals of date and time. The calculation of these tables was one of the first applications of mechanical computers. Modern ephemerides are often provided in electronic form. However, printed ephemerides are still produced, as they are useful when computational devices ar

calendar

calendar year with 365 days

calendars used in Iran

class of computer bugs related to dates beginning in the year 2000

extra full moon that appears in a subdivision of a year: either the third of four full moons in a season, or a second full moon in a month of the common calendar

special calendar used to count the days of Advent in anticipation of Christmas

period of very close to 19 years that is nearly a common multiple of the solar year and the synodic (lunar) month

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

Calendar era used in North Korea from 1997 to 2024, based on the birth of Kim Il-sung; Juche 1 = 1912 CE

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

portion of a school year ending with grade assignments

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.]]

methods of estimating a woman's fertility

calendar valid for many years

thumb|The astronomical basis of the Hindu lunar day

thumb|300px|Detail of Menologium, showing saints and martyrs of December, January and February, painted by John Tokhabi, 11th century [[tetraptych, kept at the Saint Catherine's Monastery.]] A menologium (, pl. menologia), also known by other names, is any collection of information arranged according to the days of a month, usually a set of such collections for all the months of the year. In particular, it is used for ancient Roman farmers' almanacs (); for the untitled Old English poem on the Julian calendar that appears in a manuscript of the Anglo-Saxon Chronicle; for the liturgical books (

EU's annual theme

stationery

solstice that occurs each December (winter solstice in Northern Hemisphere and summer solstice in Southern Hemisphere)

Nepalese Traditional Calendar

solstice that occurs each June (summer solstice in Northern Hemisphere and winter solstice in Southern Hemisphere)

calendar

position of the year within the 19-year Metonic cycle

Solar and lunar calendars used in Thailand

calendar used within a country for civil, official, or administrative purposes

28-year cycle of the Julian calendar

calendar designation which indicates that a period expires when the date passes everywhere on Earth

a period of 76 years

harvest-based calendar system

potential problem involving computers and computer systems in Taiwan in the year 2011 (Minguo 100)

names of Macedonian months

showing more than just the time of day

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.

Latin work written by Bede

aspect of history of how people have used calendars in methods for keeping track of days and larger divisions of time

Traditional calendar of the Mongols

Traditional rhyme

In astronomy, an octaeteris (, plural: octaeterides) is the period of eight solar years after which the moon phase occurs on the same day of the year plus one or two days.

Barbanera is a famous Italian almanac, printed for the first time in 1762 and still published yearly today.

World Days or International Days observed at UNESCO designated by United Nations General Assembly

type of pictorial histories created by various Plains tribes in North America

British parliament act of 1750 introducing the Gregorian Calendar in Great Britain and possessions from September 1752

Texts from Qumran

Persian definition in astronomy

ancient or modern calendar of Georgia

astronomical cycle he created

mnemonic for the lengths of the months of the year in the Gregorian and Julian calendars