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Encyclopedia > Epoch (reference date)

In chronology, an epoch (or epochal date, or epochal event) means an instant in time chosen as the origin of a particular era. The epoch serves as a reference point from which time is measured. Time measurement units are counted from the epoch so that the date and time of events can be specified unambiguously. Events taking place before the epoch can be dated by counting negatively from the epoch. For the novel by Michael Crichton, see Timeline (novel). ... Era may refer to: Era, a long period of history ERA Real Estate, also known as Electronic Realty Associates Inc. ... A pocket watch, a device used to tell time Look up time in Wiktionary, the free dictionary. ...


Epochs are generally chosen to be convenient or significant by a consensus of the time scale's initial users, or by authoritarian fiat.

Contents

Calendars

Each calendar era starts from an arbitrary epoch, which is often chosen to commemorate an important historical or mythological event. For example, the epoch of the anno Domini calendar era (the civil calendar era used internationally and in many countries) is the traditionally-reckoned Incarnation of Jesus.[1] Thus, the first instant of January 1, AD 2006 should be exactly 2005 years since the epoch (incomplete information about how the traditional epoch was chosen, combined with quirks in the development of the modern Gregorian calendar make this technically incorrect). Many other current and historical calendar eras exist, each with its own epoch. A calendar era is the year numbering system used by a calendar. ... Dionysius Exiguus invented Anno Domini years to date Easter. ... Look up Incarnation in Wiktionary, the free dictionary Incarnation, which literally means enfleshment, refers to the conception, and live birth of a sentient creature (generally human) who is the material manifestation of an entity or force whose original nature is immaterial. ... This article is about Jesus of Nazareth. ... January 1 is the first day of the calendar year in both the Julian and Gregorian calendars. ... Dionysius Exiguus invented Anno Domini years to date Easter. ... For the Manfred Mann album, see 2006 (album). ... The Gregorian calendar is the most widely used calendar in the world. ... Era Vulgaris redirects here. ...


Asian national eras

Japanese era name (年号, nengō, lit. ... For the CPR ocean liner, see Empress of Japan. ... Today, the Republic of China is commonly known as Taiwan or Chinese Taipei. Not to be confused with the Peoples Republic of China. ... 1912 (MCMXII) was a leap year starting on Monday in the Gregorian calendar (or a leap year starting on Tuesday in the 13-day-slower Julian calendar). ... Manse Manse! Kim Jong Il! The Juche Idea (also Juche Sasang or Chuche; pronounced // in Korean, approximately joo-cheh) is the official state ideology of North Korea and the political system based on it. ... Kim Il-sung (15 April 1912 – 8 July 1994) was the leader of North Korea from its founding in 1948 until his death, when he was succeeded by his son Kim Jong-il. ... An autarky is an economy that limits trade with the outside world, or an ecosystem not affected by influences from the outside, and relies entirely on its own resources. ... His Majesty King Rama V of Siam, with his son, HRH Crown Prince Maha Vajirunnahis (portrait in National History Museum, Bangkok) King Chulalongkorn the Great or Rama V (royal name: Phra Chula Chomklao Chaoyuhua; Thai script: พระบาทสมเด็จพระจุลจอมเกล้าเจ้าอยู่หัว) (September 20, 1853 - October 23, 1910) was the fifth king of the Chakri dynasty... This article or section does not adequately cite its references or sources. ... April 6 is the 96th day of the year in the Gregorian calendar (97th in leap years). ... 1782 was a common year starting on Tuesday (see link for calendar). ... For the movie, see 1941 (film). ... Field Marshal Plaek Pibulsonggram (July 14, 1897–June 11, 1964) (Thai แปลก พิบูลสงคราม or ป. พิบูลสงคราม, lastname sometimes spelled Phibunsongkhram, Phibul Songkhram or Pibul Songgram) was Prime Minister and military dictator of Thailand from 1938 to 1944 and 1948 to 1957. ... The Thai solar, or Suriyakati (สุริยคติ), calendar is used in traditional and official contexts in Thailand, although the Western calendar is sometimes used in business. ... The Buddhist calendar is used on mainland southeast Asia in the countries of Cambodia, Laos, Thailand, and Myanmar (formerly Burma) in several related forms. ... The Chinese calendar is a lunisolar calendar, akin to the Hebrew calendar & Hindu Calendar, incorporating elements of a lunar calendar with those of a solar calendar. ... Yellow Emperor The Yellow Emperor or Huang Di (Traditional Chinese: , Simplified Chinese: , pinyin: huángdì) is a legendary Chinese sovereign and cultural hero who is said to be the ancestor of all Han Chinese. ...

Religious eras

  • In Israel, the traditional Hebrew calendar, using an era dating from Creation, is the official calendar. However, the Gregorian calendar is the de facto calendar and is commonly used. Government documents usually display a dual date. According to Jewish tradition, the world was created in approximately 3761 BC, corresponding to the year 0 in the Hebrew calendar. Therefore, the date, as of Rosh Hashanah in 2006, is 5767 years since the Creation of the world. [2] [3]
  • In the Islamic world, traditional Islamic dating according to the Anno Hegiræ (in the year of the hijra) or AH era remains in use to a varying extent, especially for religious purposes. The official Iranian calendar (used in Afghanistan as well as Iran) also dates from the hijra, but as it is a solar calendar its year numbering does not coincide with the religious calendar.

The Hebrew calendar (Hebrew: ‎) or Jewish calendar is the annual calendar used in Judaism. ... A calendar era is the year numbering system used by a calendar. ... This article is about the Jewish holiday of Rosh Hashanah. ... Creation according to Genesis refers to the description of the creation of the heavens and the earth by God, as described in Genesis, the first book of the Bible. ... Islam (Arabic:  ) is a monotheistic religion based upon the teachings of Muhammad, a 7th century Arab religious and political figure. ... The Islamic calendar or Muslim calendar (Arabic: التقويم الهجري; at-taqwÄ«m al-hijrÄ«; Persian: گاه‌شماری هجري قمری ‎ Gāhshomāri-ye hejri-ye qamari; also called the Hijri calendar) is the calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to... For other uses, see Hijra. ... The Iranian calendar (Persian: ‎) also known as Persian calendar or the Jalāli Calendar is a solar calendar currently used in Iran and Afghanistan. ... A solar calendar is a calendar whose dates indicate the position of the earth on its revolution around the sun (or equivalently the apparent position of the sun moving on the celestial sphere). ...

Other

A French Revolutionary Calendar in the Historical Museum of Lausanne. ... 1793 was a common year starting on Tuesday (see link for calendar). ... September 22 is the 265th day of the year in the Gregorian calendar (266th in leap years). ... 1792 was a leap year starting on Sunday (see link for calendar). ... Motto: (Liberty, equality, brotherhood, or death!) Anthem: La Marseillaise (unofficial) Capital Paris Language(s) French Government Republic Various  - 1792-1795 National Convention (rule by legislature)  - 1794-1799 Directory  - 1799-1804 First Consul Napoleon Bonaparte Legislature National Convention French Directory French Consulate History  - Storming of the Bastille/French Revolution 14 July...

Astronomy

Main article: Epoch (astronomy)

In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. The current standard epoch is J2000.0. In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... In astronomy, a celestial coordinate system is a coordinate system for mapping positions in the sky. ... The elements of an orbit are the parameters needed to specify that orbit uniquely, given a model of two ideal masses obeying the Newtonian laws of motion and the inverse-square law of gravitational attraction. ... It has been suggested that this article or section be merged into Julian epoch. ...


Computing

In computers, time is often expressed as the number of seconds or days (including a fraction) since midnight, Universal Time, on a conventional epoch defined by the operating system. Contrary to human calendars, computers usually start counting from 0 at the epoch instant. Famous epoch dates include: A BlueGene supercomputer cabinet. ... In computer science and computer programming, system time represents a computer systems notion of the passing of time. ... Universal Time (UT) is a timescale based on the rotation of the Earth. ... An operating system (OS) is a set of computer programs that manage the hardware and software resources of a computer. ...

System time is measured in seconds or ticks of arbitrary length past the epoch. Unspecified problems may occur when this number exceeds a predefined capacity, which is not necessarily a rare event; on a machine counting 10 ticks per second, a signed 32-bit count of ticks allows for only 6.8 years of accurate timekeeping. The 1-tick-per-second clock of Unix will overflow on January 19, 2038, creating the Year 2038 problem on systems that still store time as a 32-bit signed integer. David Mills, author of NTP, acknowledges that the protocol's ultra-precise 64-bit timestamps will roll over on February 6, 2036 and advises that: January 1 is the first day of the calendar year in both the Julian and Gregorian calendars. ... This article is about the year 1. ... Symbian OS is an operating system with associated libraries, user interface frameworks and reference implementations of common tools, produced by Symbian. ... Microsoft . ... REXX (REstructured eXtended eXecutor) is an interpreted programming language which was developed at IBM. It is a structured high-level programming language which was designed to be both easy to learn and easy to read. ... The Julian day or Julian day number (JDN) is the (integer) number of days that have elapsed since Monday, January 1, 4713 BC in the proleptic Julian calendar [1]. That day is counted as Julian day zero. ... January 1 is the first day of the calendar year in both the Julian and Gregorian calendars. ... Events February 8 - Robert Devereux, 2nd Earl of Essex, rebels against Elizabeth I of England - revolt is quickly crushed February 25 - Robert Devereux beheaded Jesuit Matteo Ricci arrives in China Bad harvest in Russia due to rainy summer Dutch troops drive Portuguese from Málaga Battle of Kinsale, Ireland Births... Microsoft Windows is the name of several families of proprietary software operating systems by Microsoft. ... Windows API is a set of APIs, (application programming interfaces) available in the Microsoft Windows operating systems. ... 17 November is also the name of a Marxist group in Greece, coinciding with the anniversary of the Athens Polytechnic uprising. ... 1858 (MDCCCLVIII) is a common year starting on Friday of the Gregorian calendar (or a common year starting on Sunday of the 12-day-slower Julian calendar). ... OpenVMS[1] (Open Virtual Memory System or just VMS) is the name of a high-end computer server operating system that runs on the VAX[2] and Alpha[3] family of computers developed by Digital Equipment Corporation of Maynard, Massachusetts (DIGITAL was then purchased by Compaq, and is now owned... The Julian day or Julian day number (JDN) is the (integer) number of days that have elapsed since Monday, January 1, 4713 BC in the proleptic Julian calendar [1]. That day is counted as Julian day zero. ... An ephemeris (plural: ephemerides) (from the Greek word ephemeros= daily) was, traditionally, a table providing the positions (given in a Cartesian coordinate system, or in right ascension and declination or, for astrologers, in longitude along the zodiacal ecliptic), of the Sun, the Moon, and the planets in the sky at... Aerial view of USNO. The United States Naval Observatory (USNO) is one of the oldest scientific agencies in the United States. ... December 31 is the 365th day of the year (366th in leap years) in the Gregorian Calendar. ... Year 1899 (MDCCCXCIX) was a common year starting on Sunday (link will display the full calendar). ... This article or section does not adequately cite its references or sources. ... The Julian calendar was introduced in 46 BC by Julius Caesar and came into force in 45 BC (709 ab urbe condita). ... There are very few or no other articles that link to this one. ... The Gregorian calendar is the most widely used calendar in the world. ... December 30 is the 364th day of the year (365th in leap years) in the Gregorian Calendar, with 1 day remaining. ... Year 1899 (MDCCCXCIX) was a common year starting on Sunday (link will display the full calendar). ... January 1 is the first day of the calendar year in both the Julian and Gregorian calendars. ... Year 1900 (MCM) was an exceptional common year starting on Monday (link will display the full calendar) of the Gregorian calendar, but a leap year starting on Saturday of the Julian calendar. ... The Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. ... January 1 is the first day of the calendar year in both the Julian and Gregorian calendars. ... 1904 (MCMIV) was a leap year starting on a Friday (see link for calendar). ... Time zones are areas of the Earth that have adopted the same standard time, usually referred to as the local time. ... The first Macintosh computer, introduced in 1984, upgraded to a 512K Fat Mac. The Macintosh or Mac, is a line of personal computers designed, developed, manufactured, and marketed by Apple Computer. ... Sherlock 2 for Mac OS 9 with the new metallic appearance Mac OS 9, introduced by Apple Computer on 1999-10-23, is the last version of the Classic Macintosh Operating System (Mac OS) released before being succeeded by Mac OS X. Upon introduction, Mac OS 9 was advertised as... Palm OS is a compact operating system developed and licensed by PalmSource, Inc. ... January 1 is the first day of the calendar year in both the Julian and Gregorian calendars. ... 1970 (MCMLXX) was a common year starting on Thursday. ... Unix time, or POSIX time, is a system for describing points in time: it is the number of seconds elapsed since midnight UTC on the morning of January 1, 1970, not counting leap seconds. ... Mac OS X (official IPA pronunciation: ) is a line of proprietary, graphical operating systems developed, marketed, and sold by Apple Inc. ... Java is an object-oriented applications programming language developed by Sun Microsystems in the early 1990s. ... January 1 is the first day of the calendar year in both the Julian and Gregorian calendars. ... 1978 (MCMLXXVIII) was a common year starting on Sunday. ... AmigaOS is the default native operating system of the Amiga personal computer. ... January 1 is the first day of the calendar year in both the Julian and Gregorian calendars. ... 1980 (MCMLXXX) was a leap year starting on Tuesday. ... MS-DOS (for Microsoft Disk Operating System) is an operating system commercialized by Microsoft. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... File Allocation Table (FAT) is a partially patented file system developed by Microsoft for MS-DOS and was the primary file system for consumer versions of Microsoft Windows up to and including Windows Me. ... January 6 is the 6th day of the year in the Gregorian calendar, with 359 days (360 in leap years) remaining. ... 1980 (MCMLXXX) was a leap year starting on Tuesday. ... Qualcomm (NASDAQ: QCOM) is a wireless telecommunications research and development company based in San Diego, California. ... BREW is an application development platform created by Qualcomm for mobile phones. ... The Global Positioning System (GPS) is currently the only fully functional Global Navigation Satellite System (GNSS). ... In computer science, to simplify the specification and allow some flexibility in implementation, the specification sometimes defines a behavior undefined. ... The term arithmetic overflow or simply overflow has the following meanings. ... January 19 is the 19th day of the year in the Gregorian calendar. ... 2038 (MMXXXVIII) will be a common year starting on Friday of the Gregorian calendar. ... In computing, the year 2038 problem may cause some computer software to fail in or about the year 2038. ... David L. Mills (born June 3, 1938) was the first head of the Internet Architecture Board. ... The Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. ... February 6 is the 37th day of the year in the Gregorian calendar. ... 2036 (MMXXXVI) will be a leap year starting on Tuesday of the Gregorian calendar. ...

Should NTP be in use in 2036, some external means will be necessary to qualify time relative to 1900 and time relative to 2036 (and other multiples of 136 years). (quoted from RFC 1305)

The evolving definition of official time over history introduces more subtle problems for computer-based linear representations. Leap years and the Gregorian calendar are generally taken into account, but leap seconds are more challenging due to their non-linear rate of past occurrences and the impossibility to accurately predict their future occurrences. These complications are discussed at length in the Unix time article. A leap year (or intercalary year) is a year containing an extra day or month in order to keep the calendar year in sync with an astronomical or seasonal year. ... The Gregorian calendar is the most widely used calendar in the world. ... A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ... Unix time, or POSIX time, is a system for describing points in time: it is the number of seconds elapsed since midnight UTC on the morning of January 1, 1970, not counting leap seconds. ...


Trivia

  • According to Martin Minow,
January 1, 1904, was chosen as the base for the Macintosh clock because it was the first leap year of the twentieth century. [...] This means that by starting with 1904, Macintosh system programmers could save a half dozen instructions in their leap-year checking code, which they thought was way cool.
  • The fictional (or Julian) leap day February 29, 1900 in Microsoft Excel was introduced intentionally in order to maintain compatibility with then market leader Lotus 1-2-3. Designers of Lotus 1-2-3 had probably chosen this simplified behaviour in order to save some precious processing time and program space. For the rest of its time range 1900 - 9999 Excel uses the Gregorian calendar, hence e.g. there is no February 29, 2100.
  • Microsoft Excel (and Lotus 1-2-3) technically consider the epoch of December 31, 1899 as January 0, 1900 or a serial date of zero (consequently, December 31, 1899 cannot be used). January 0, 1900 can be processed and formatted in Excel Worksheets, just as any other date.

The Julian calendar was introduced in 46 BC by Julius Caesar and came into force in 45 BC (709 ab urbe condita). ... There are very few or no other articles that link to this one. ... This article or section does not adequately cite its references or sources. ... Lotus 1-2-3 is a spreadsheet program from Lotus Software (now part of IBM). ... February 29th, or bissextile day, is the 60th day of a leap year in the Gregorian Calendar, with 306 days remaining. ... 2100 can refer to either: The year at the end of the 21st century. ... December 31 is the 365th day of the year (366th in leap years) in the Gregorian Calendar. ... Year 1899 (MDCCCXCIX) was a common year starting on Sunday (link will display the full calendar). ...

Notes

  1. ^ Blackburn, B. & Holford-Strevens, L. (2003). The Oxford Companion to the Year: An exploration of calendar customs and time-reckoning. Oxford University Press. Glossary entry for "Incarnation era", p. 881.
  2. ^ My Jewish Learning:Counting the Years
  3. ^ Rosetta Calendar

External links

  • RFC 1305, defining the Network Time Protocol, includes a lot of information on time standards in historical and modern calendars, starting on page 81 (numbered 74) of the original specification in PostScript format.
  • Critical and Significant Dates (J. R. Stockton), an extensive list of dates that are problematic for various operating systems and computing devices
  • Dates potentially causing problems in computer systems

 
 

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