Gregorian calendar in the context of Japanese New Year

The Constitution of the Year XII (French: Constitution de l’an XII), also called the Organic Sénatus-consulte of 28 Floréal, year XII (Sénatus-consulte organique du 28 floréal an XII), was a national constitution of the First French Republic adopted during the Year XII of the French Revolutionary Calendar (1804 in the Gregorian calendar).

It amended the earlier Constitution of the Year VIII and Constitution of the Year X, establishing the First French Empire with Napoleon Bonaparte — previously First Consul for Life, with wide-ranging powers — as Napoleon I, Emperor of the French. The Constitution established the House of Bonaparte as France's imperial dynasty, making the throne hereditary in Napoleon's family. The Constitution of the Year XII was later itself extensively amended by the Additional Act and definitively abolished with the final return of the Bourbons in 1815.

Common Era (CE) and Before the Common Era (BCE) are year notations for the Gregorian or Julian calendar, and are exactly equivalent to the Anno Domini (AD) and Before Christ (BC) notations. The expressions "2025 CE" and "AD 2025" each equally describe the current year; "400 BCE" and "400 BC" are the same year too. BCE/CE are primarily used to avoid religious connotations, by not referring to Jesus as Dominus [Lord].

A mnemonic device (/nəˈmɒnɪk/ nə-MON-ik), memory trick or memory device is any learning technique that aids information retention or retrieval in the human memory, often by associating the information with something that is easier to remember.

It makes use of elaborative encoding, retrieval cues and imagery as specific tools to encode information in a way that allows for efficient storage and retrieval. It aids original information in becoming associated with something more accessible or meaningful—which in turn provides better retention of the information.

A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A date is the designation of a single and specific day within such a system. A calendar is also a physical record (often paper) of such a system. A calendar can also mean a list of planned events, such as a court calendar, or a partly or fully chronological list of documents, such as a calendar of wills.

The Hijri calendar (Arabic: ٱلتَّقْوِيم ٱلْهِجْرِيّ, romanized: al-taqwīm al-hijrī), also known in English as the Islamic calendar, is a lunar calendar consisting of 12 lunar months in a year of 354 or 355 days. It is used to determine the proper days of Islamic holidays and rituals, such as the annual fasting and the annual season for the great pilgrimage. In almost all countries where the predominant religion is Islam, the civil calendar is the Gregorian calendar, with Syriac month-names used in the Levant and Mesopotamia (Iraq, Syria, Jordan, Lebanon and Palestine), but the religious calendar is the Hijri one.

This calendar enumerates the Hijri era, whose epoch was established as the Islamic New Year in 622 CE. During that year, Muhammad and his followers migrated from Mecca to Medina and established the first Muslim community (ummah), an event commemorated as the Hijrah. In the West, dates in this era are usually denoted AH (Latin: Anno Hegirae, lit. 'In the year of the Hijrah'). In Muslim countries, it is also sometimes denoted as H from its Arabic form (سَنَة هِجْرِيَّة, abbreviated ھ). In English, years prior to the Hijra are denoted as BH ("Before the Hijra").

The terms anno Domini (AD) and before Christ (BC) are used when designating years in the Gregorian and Julian calendars. The term anno Domini is Medieval Latin and means "in the year of the Lord" but is often presented using "our Lord" instead of "the Lord", taken from the full original phrase "anno Domini nostri Jesu Christi", which translates to "in the year of our Lord Jesus Christ". The form "BC" is specific to English, and equivalent abbreviations are used in other languages: the Latin form, rarely used in English, is ante Christum natum (ACN) or ante Christum (AC).

This calendar era takes as its epoch the traditionally reckoned year of the conception or birth of Jesus. Years AD are counted forward since that epoch and years BC are counted backward from the epoch. There is no year zero in this scheme; thus the year AD 1 immediately follows the year 1 BC. This dating system was devised in 525 by the Eastern Roman monk Dionysius Exiguus but was not widely used until the 9th century. Modern scholars believe that the actual date of birth of Jesus was about 5 BC.

The French Republican calendar (French: calendrier républicain français), also commonly called the French Revolutionary calendar (calendrier révolutionnaire français), was a calendar created and implemented during the French Revolution and used by the French government for about 12 years from late 1793 to 1805, and for 18 days by the Paris Commune in 1871, meant to replace the Gregorian calendar. The calendar consisted of twelve 30-day months, each divided into three 10-day cycles similar to weeks, plus five or six intercalary days at the end to fill out the balance of a solar year. It was designed in part to remove all religious and royalist influences from the calendar, and it was part of a larger attempt at dechristianisation and decimalisation in France (which also included decimal time of day, decimalisation of currency, and metrication). It was used in government records in France and other areas under French rule, including Belgium, Luxembourg, and parts of the Netherlands, Germany, Switzerland, Malta, and Italy.

The Constitution of the Year X (French: Constitution de l'an X) was a national constitution of France adopted during the Year X (10) on 16 Thermidor (4 August) of the French Revolutionary Calendar (1802 in the Gregorian calendar). It amended the Constitution of the Year VIII, revising the Consulate to augment Napoleon Bonaparte's authority by making him First Consul for Life.

Both the Constitution of the Year X and the Constitution of the Year VIII were further amended by the Constitution of the Year XII, which established the First French Empire with Napoleon as Emperor.

The Great Eastern Crisis of 1875–1878 began in the Ottoman Empire's administrative territories in the Balkan Peninsula in 1875, with the outbreak of several uprisings and wars that resulted in the intervention of international powers, and was ended with the Treaty of Berlin in July 1878.

The war is referred to differently in various languages of the peoples involved in it due to differing sociocultural backgrounds. In Serbo-Croatian and Turkish, the war is likewise referred to as Velika istočna kriza ("Great Eastern Crisis") and Şark Buhranı ("Eastern Crisis") respectively. However, the occasionally used Turkish name Ramazan Kararnamesi ("Decree of Ramadan") refers specifically to the sovereign default declared on 30 October 1875 in historiography while 93 Harbi ("War of 93") refers to the Russo-Turkish War (the year 1293 of the Islamic Rumi calendar corresponding to the year 1877 on the Gregorian calendar).

The Babylonian calendar was a lunisolar calendar used in Mesopotamia from around the 2nd millennium BC until the Seleucid Era (294 BC), and it was specifically used in Babylon from the Old Babylonian Period (1780s BC) until the Seleucid Era.

In the Seleucid Era it was reformed as "Greek time", Anno Graecorum was introduced and used in the Middle East and Egypt until the middle of the first millennium when the First Council of Nicaea AD 325 defined the Church year based on the Roman early Julian calendar. As Anno Graecorum formed the basis for time references in the Bible and spread westward, it rather increased the Babylonian calendars importance. The Babylonian calendar is also partly reflected in calendars in South and East Asia and the Islamic calendar as well as Iranian calendars. The Julian calendar inherited the definitions of the 12 month system, week, hour etc. from the Babylonian calendar and the current Jewish calendar can be seen as a slightly modified Babylonian calendar that still exists today and is practised, but with Anno Mundi Livryat haOlam year calculation since the creation of the world. Today's global time system UTC (Gregorian calendar) therefore has its main structure inherited from the Babylonian calendar.

Hajj (/hɑːdʒ/; Arabic: حَجّ, romanized: Ḥajj; also spelled Hadj or Haj) is an annual Islamic pilgrimage to Mecca, Saudi Arabia, the holiest city for Muslims. Hajj is a mandatory religious duty for capable Muslims that must be carried out at least once in their lifetime by all adult Muslims who are physically and financially capable of undertaking the journey, and of supporting their family during their absence from home.

In Islamic terminology, Hajj is a pilgrimage made to the Kaaba, the "House of Allah", in the sacred city of Mecca in Saudi Arabia. It is one of the Five Pillars of Islam, alongside Shahadah (oath that one believes there is no god but Allah), salat (prayer), zakat (almsgiving), and sawm (fasting during Ramadan). The Hajj is an annual practice when Muslim brotherhood is on display and their solidarity with fellow Muslim people and submission to God (Allah) is fulfilled. The Hajj is taken by Muslims to cleanse their souls of all worldly sins, which connotes both the outward act of a journey after death and the inward act of good intentions. The rites of pilgrimage are performed over five to six days, extending from the 8th to the 12th or 13th of Dhu al-Hijjah, the last month of the Islamic calendar. Because the Islamic calendar is lunar and the Islamic year is about eleven-twelve days shorter than the Gregorian year, the Gregorian date of Hajj changes from year to year. In 2024 AD (1445 AH), Dhu al-Hijjah extended from 7 June to 6 July and in 2025 AD (1446 AH), Dhu al-Hijjah was from 28 May to 25 June. In 2026 AD (1447 AH), Dhu al-Hijjah will extend from 18 May to 15 June; and in 2027 AD (1448 AH), Dhu al-Hijjah will extend from 24 May to 22 June.

A year is a unit of time based on how long it takes the Earth to orbit the Sun. In scientific use, the tropical year (approximately 365 solar days, 5 hours, 48 minutes, 45 seconds) and the sidereal year (about 20 minutes longer) are more exact. The modern calendar year, as reckoned according to the Gregorian calendar, approximates the tropical year by using a system of leap years.

The term 'year' is also used to indicate other periods of roughly similar duration, such as the lunar year (a roughly 354-day cycle of twelve of the Moon's phases – see lunar calendar), as well as periods loosely associated with the calendar or astronomical year, such as the seasonal year, the fiscal year, the academic year, etc.

The Julian calendar is a solar calendar of 365 days in every year with an additional leap day every fourth year (without exception). The Julian calendar is still used as a religious calendar in parts of the Eastern Orthodox Church and in parts of Oriental Orthodoxy as well as by the Amazigh people (also known as the Berbers). For a quick calculation, between 1901 and 2099 the much more common Gregorian date equals the Julian date plus 13 days.

The Julian calendar was proposed in 46 BC by (and takes its name from) Julius Caesar, as a reform of the earlier Roman calendar, which was largely a lunisolar one. It took effect on 1 January 45 BC, by his edict. Caesar's calendar became the predominant calendar in the Roman Empire and subsequently most of the Western world for more than 1,600 years, until 1582 when Pope Gregory XIII promulgated a revised calendar. Ancient Romans typically designated years by the names of ruling consuls; the Anno Domini system of numbering years was not devised until 525, and became widespread in Europe in the eighth century.

The December solstice, also known as the southern solstice, is the solstice that occurs each December – typically on 21 December, but may vary by one day in either direction according to the Gregorian calendar. In the Northern Hemisphere, the December solstice is the winter solstice (the day with the shortest period of daylight), whilst in the Southern Hemisphere it is the summer solstice (the day with the longest period of daylight). During December solstice, the Sun is directly over the Tropic of Capricorn, located in the Southern Hemisphere.

The December solstice is often seen as the middle of winter in the Northern Hemisphere and the middle of summer in the Southern Hemisphere.

The March equinox or northward equinox is the equinox on the Earth when the subsolar point appears to leave the Southern Hemisphere and cross the celestial equator, heading northward as seen from Earth. The March equinox is known as the vernal equinox (or spring equinox) in the Northern Hemisphere and as the autumnal equinox (or fall equinox) in the Southern Hemisphere.

On the Gregorian calendar at 0° longitude, the northward equinox usually occurs on March 20. However, it can occur as early as March 19 (which happened most recently in 1796, and will happen next in 2044), and it can occur as late as March 21 (which happened most recently in 2007, and will happen next in 2102). For a common year the computed time slippage is about 5 hours 49 minutes later than the previous year, and for a leap year about 18 hours 11 minutes earlier than the previous year. Balancing the increases of the common years against the losses of the leap years keeps the calendar date of the March equinox from drifting more than one day from March 20 each year.

March is the third month of the year in both the Julian and Gregorian calendars. Its length is 31 days. In the Northern Hemisphere, the meteorological beginning of spring occurs on the first day of March. The March equinox on the 20 or 21 marks the astronomical beginning of spring in the Northern Hemisphere and the beginning of autumn in the Southern Hemisphere, where September is the seasonal equivalent of the Northern Hemisphere's March.

The June solstice is the solstice on Earth that occurs annually between 20 and 22 June according to the Gregorian calendar. In the Northern Hemisphere, the June solstice is the summer solstice (the day with the longest period of daylight), while in the Southern Hemisphere it is the winter solstice (the day with the shortest period of daylight). It is also known as the northern solstice or summer solstice. During the June solstice, the Sun is directly over the Tropic of Cancer, located in the northern hemisphere.