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Julian Day

Julian day

The Julian day or Julian day number (JDN) is the number of days that have elapsed since 12 noon Greenwich Mean Time (UT or TT) on Monday, January 1, 4713 BC in the proleptic Julian calendar . That day is counted as Julian day zero. The Julian day system was intended to provide astronomers with a single system of dates that could be used when working with different calendars and to unify different historical chronologies.

Julian Date

The Julian Date (JD) is the Julian day number plus the decimal fraction of the day that has elapsed since noon. Historical Julian Dates were recorded relative to GMT or Ephemeris Time, but the International Astronomical Union now recommends that Julian Dates be specified in Terrestrial Time, and that when necessary to specify Julian Dates using a different time scale, that the time scale used be indicated when required, such as JD(UT1). The fraction of the day is found by converting the number of hours, minutes, and seconds after noon into the equivalent decimal fraction. The term Julian date is also used to refer to:
- Julian calendar dates
- ordinal dates (day-of-year) The use of Julian date to refer to the day-of-year (ordinal date) is usually considered to be incorrect.

Alternatives

- The Heliocentric Julian Day (HJD) is the same as the Julian day, but adjusted to the frame of reference of the Sun, and thus can differ from the Julian day by as much as 8.3 minutes, that being the time it takes the Sun's light to reach Earth. The Julian day is sometimes referred to as the Geocentric Julian Day (GJD) in order to distinguish it from HJD.
- Another version of the Julian day, introduced by Peter Meyer, is the chronological Julian Day (CJD), in which the starting point is set at midnight at the beginning of January 1, 4713 BC (proleptic Julian calendar) local time rather than noon UT. Chronographers found the Julian day concept useful, but they didn't like noon as the starting time. So CJD = JD + 0.5 (in the Greenwich time zone, anyway). Note that JD may use Universal Time (UT) or Terrestrial Time (TT), and so it is the same for all time zones and is independent of Summer Time or Daylight-Saving Time (DST). On the other hand, CJD is not, so it changes with different time zones and takes into account the different local DSTs. Users of CJD sometimes refer to the Julian day as astronomical Julian Day (AJD) to distinguish it from CJD. Because the starting point is so long ago, numbers in the Julian day can be quite large and cumbersome. A more recent starting point is sometimes used, for instance by dropping the leading digits, in order to fit into limited computer memory with an adequate amount of precision.
- The Modified Julian Day (MJD), introduced by the Smithsonian Astrophysical Observatory in 1957 to record the orbit of Sputnik, is defined in terms of the Julian day as follows: ::MJD = JD - 2400000.5 :The offset of 0.5 means that MJD started at midnight at the beginning of November 17, 1858, and that every Modified Julian Day begins and ends at midnight UT or TT.
- The Reduced Julian Day (RJD) is also used by astronomers and counts days from the same day as MJD, but from noon UT or TT, and thus is defined as: : RJD = JD - 2400000
- The Truncated Julian Day (TJD) was introduced by NASA for the space program. TJD began at May 24, 1968. Since TJD exceeded four digits on October 10, 1995, some now count TJD from this date in order to maintain a four-digit number. It can be defined as: ::TJD = JD - 2440000.5 :or ::TJD = (JD - 0.5) mod 10000
- The Dublin Julian Day (DJD) is a count of days from midnight at the beginning of January 1, 1900. The source of the name is unknown. It is used in computer programs, such as Lotus 1-2-3 and Microsoft Excel. In these particular programs, this date is counted as day 1, instead of day 0, because the year 1900 was [http://support.microsoft.com/default.aspx?scid=kb;en-us;214326 erroneously] treated as a leap year.
- The Lilian day number defines day 1 as October 15, 1582, which was the first day of the Gregorian Calendar. It was named for Aloysius Lilius, the principal author of the Gregorian Calendar.
- The ANSI Date defines January 1, 1601 as day 1, and is used as the origin of COBOL integer dates. This epoch is the beginning of the previous 400-year cycle of leap years in the Gregorian Calendar, which ended with the year 2000.
- Rata Die is the epoch used in Calendrical Calculations by Edward M. Reingold and Nachum Dershowitz, where day 1 is January 1, 1, that is, the first day of the Christian or Common Era in the proleptic Gregorian Calendar.

History

The Julian day number is based on the Julian Period proposed by Joseph Scaliger in 1583, at the time of the Gregorian calendar reform, but it is the multiple of three calendar cycles used with the Julian calendar: : 15 (indiction cycle) × 19 (Metonic cycle) × 28 (Solar cycle) = 7980 years Its epoch falls at the last time when all three cycles were in their first year together — Scaliger chose this because it pre-dated all historical dates. Note: although many references say that the "Julian" in "Julian day" refers to Scaliger's father, Julius Scaliger, in the introduction to Book V of his Opus de Emendatione Tempore (Work on the Emendation of Time) he states: "Iulianum vocauimus: quia ad annum Iulianum dumtaxat accomodata est" which translates more or less as "We call this Julian merely because it is accommodated to the Julian year". This "Julian" refers to Julius Caesar, who introduced the Julian calendar in 46 BC. In his book Outlines of Astronomy, first published in 1849, the astronomer John Herschel wrote:

The first year of the current Julian period, or that of which the number in each of the three subordinate cycles is 1, was the year 4713 B.C., and the noon of the 1st of January of that year, for the meridian of Alexandria, is the chronological epoch, to which all historical eras are most readily and intelligibly referred, by computing the number of integer days intervening between that epoch and the noon (for Alexandria) of the day, which is reckoned to be the first of the particular era in question. The meridian of Alexandria is chosen as that to which Ptolemy refers the commencement of the era of Nabonassar, the basis of all his calculations.

Astronomers adopted Herschel's Julian Days in the late 19th century, but using the meridian of Greenwich instead of Alexandria, after the former was made the Prime Meridian by international conference in 1884. This has now become the standard system of Julian days. Julian days are typically used by astronomers to date astronomical observations, thus eliminating the complications resulting from using standard calendar periods like eras, years, months, or weeks. Julian days begin at noon because when Herschel recommended them, the astronomical day began at noon (it did so until 1925). The astronomical day had begun at noon ever since Ptolemy chose to begin the days in his astronomical periods at noon. He chose noon because the transit of the Sun across the observer's meridian occurs at the same apparent time every day of the year, unlike sunrise or sunset, which vary by several hours. Midnight was not even considered because it could not be accurately determined using water clocks. Nevertheless, he double dated most nighttime observations with both Egyptian days beginning at sunrise and Babylonian days beginning at sunset. Thus the astronomical day did not begin at noon to allow all observations of a single night to be in a single day.

Calculation

The Julian day number can be calculated using the following formulas: All divisions (except for JD) are integer divisions, meaning the remainder in the division is discarded. The months January to December are 1 to 12. Astronomical year numbering is used, thus 1 BC is 0, 2 BC is −1, and 4713 BC is −4712.

\begina & = &  \\ \\y & = & year + 4800 - a \\ \\m & = & month + 12a - 3 \\\end

For a date in the Gregorian calendar (at noon):

\beginJDN & = & day +  + 365y +  -  +  - 32045\end

For a date in the Julian calendar (at noon):

\beginJDN & = & day +  + 365y +  - 32083\end

For the full Julian Date, not counting leap seconds (divisions are real numbers):

\beginJD & = & JDN +  +  + \end

So, for example, 1 January 2000 at midday corresponds to JD = 2451545.0 The day of the week can be determined from the Julian day number by calculating it modulo 7, where 0 means Monday.

Other Usages

The Julian Dating system may be the basis of the "Stardate" used in the Television series Star Trek. The character, James T. Kirk, was usually the one to recite the Stardate when an excerpt of his Captain's Log plays at the beginning of many of the episodes. It has since then been replaced by another Stardating system when Star Trek: The Next Generation introduced their own dating system consisting of 5 numbers, however retaining the decimal fraction value of the Julian dating system.

Footnotes

- This equals November 24, 4714 BC in the proleptic Gregorian calendar.

References

- Gordon Moyer, "The Origin of the Julian Day System," Sky and Telescope 61 (April 1981) 311-313.
- Explanatory Supplement to the Astronomical Almanac, edited by P. Kenneth Seidelmann. University Science Books, 1992. ISBN 0935702687

External links

- [http://hermetic.nofadz.com/cal_stud/jdn.htm Article 'Julian Day Numbers'] by Peter Meyer
- [http://aa.usno.navy.mil/data/docs/JulianDate.html U.S. Naval Observatory Julian Date Converter]
- [http://www.nr.com/julian.html Julian Day and Civil Date calculator]
- [http://tycho.usno.navy.mil/mjd.html U.S. Naval Observatory Time Service article]
- [http://visualiseur.bnf.fr/Visualiseur?Destination=Gallica&O=NUMM-94926 Outlines of Astronomy by John Herschel]
- [http://www.iers.org/iers/earth/resolutions/UAI_b1.html International Astronomical Union Resolution 1B: On the Use of Julian Dates]
- [http://emr.cs.iit.edu/home/reingold/calendar-book/Calendrica.html Calendrica]
- [http://isotropic.org/uw/date/ Another Julian Day calculator with conversions to many other calendars] valid from 1 January 100 proleptic Gregorian calendar
- [http://sourceforge.net/projects/solarclock/ Open-source date conversion software] Category:Calendars Category:Celestial mechanics ja:ユリウス通日

Day

:The Day language is spoken in Chad. A day (symbol: d) is a unit of time. It is not an SI unit but it is accepted for use with SI. The SI unit of time is the second. It has several definitions.

Definition of a day in SI

There is one day for every 86,400 SI seconds.

Definition of a day in astronomy

For a given planet, there are two types of day defined in astronomy: 1 apparent sidereal day = a single rotation of a planet with respect to the distant stars (for Earth it is 23.934 solar hours or 24 sidereal hours) 1 solar day = a single rotation of a planet with respect to Sun.

Origin

The term comes from the Old English dæg, with similar terms common in all other Indo-European languages, such as dies in Latin and dive in Sanskrit.

Colloquial definition of day

The word refers either to the period of light when the Sun is above the local horizon or to the full day covering a dark and a light period. The latter is sometimes called a nychthemeron in English, from the Greek for night-day. Greek painting by Peter Nicolai Arbo.]]

Introduction

Different definitions of the day are based on the apparent motion of the Sun across the sky (solar day; see solar time). The reason for this apparent motion is the rotation of the Earth around its axis, as well as the revolution of the Earth in its orbit around the Sun. A day, as opposed to night, is commonly defined as the period during which sunlight directly reaches the ground, assuming that there are no local obstacles. Two effects make days on average longer than nights. The Sun is not a point, but has an apparent size of about 32 minutes of arc. Additionally, the atmosphere refracts sunlight in such a way that some of it reaches the ground even when the Sun is below the horizon by about 34 minutes of arc. So the first light reaches the ground when the centre of the Sun is still below the horizon by about 50 minutes of arc. The difference in time depends on the angle at which the Sun rises and sets (itself a function of latitude), but amounts to almost seven minutes at least. Ancient custom has a new day start at either the rising or setting of the Sun on the local horizon (Italian reckoning, for example). The exact moment of, and the interval between, two sunrises or two sunsets depends on the geographical position (longitude as well as latitude), and the time of year. This is the time as indicated by ancient hemispherical sundials. A more constant day can be defined by the Sun passing through the local meridian, which happens at local noon (upper culmination) or midnight (lower culmination). The exact moment is dependent on the geographical longitude, and to a lesser extent on the time of the year. The length of such a day is nearly constant (24 hours ± 30 seconds). This is the time as indicated by modern sundials. A further improvement defines a fictitious mean Sun that moves with constant speed along the celestial equator; the speed is the same as the average speed of the real Sun, but this removes the variation over a year as the Earth moves along its orbit around the Sun (due to both its velocity and its axial tilt). The Earth's day has increased in length over time. The original length of one day, when the Earth was new about 4.5 billion years ago, was about six hours as determined by computer simulation. It was 21.9 hours 620 million years ago as recorded by rhythmites (alternating layers in sandstone). This phenomenon is due to tides raised by the Moon which slow Earth's rotation. Because of the way the second is defined, the mean length of a day is now about 86,400.002 seconds, and is increasing by about 1.7 milliseconds per century (an average over the last 2700 years). See tidal acceleration for details.

Civil day

For civil purposes a common clock time has been defined for an entire region based on the mean local solar time at some central meridian. Such time zones began to be adopted about the middle of the 19th century when railroads with regular schedules came into use, with most major countries having adopted them by 1929. For the whole world, 39 such time zones are now in use. The main one is "world time" or UTC (Coordinated Universal Time). The present common convention has the civil day starting at midnight, which is near the time of the lower culmination of the mean Sun on the central meridian of the time zone. A day is commonly divided into 24 hours of 60 minutes of 60 seconds each.

Leap seconds

In order to keep the civil day aligned with the apparent movement of the Sun, leap seconds may be inserted. A civil clock day is typically 86400 SI seconds long, but will be 86401 s long in the event of a leap second. Leap seconds are announced in advance by the International Earth Rotation and Reference Systems Service which measures the Earth's rotation and determines whether a leap second is necessary. Leap seconds occur only at the end of a UTC month, and have only ever been inserted at the end of June 30 or December 31.

Astronomy

In astronomy, the sidereal day is also used; it is about 3 minutes 56 seconds shorter than the solar day, and close to the actual rotation period of the Earth, as opposed to the Sun's apparent motion. In fact, the Earth spins 366 times about its axis during a 365-day year, because the Earth's revolution about the Sun removes one apparent turn of the Sun about the Earth.

Boundaries of the day

For most diurnal animals, including Homo sapiens, the day naturally begins at dawn and ends at sunset. Humans, with our cultural norms and scientific knowledge, have supplanted Nature with several different conceptions of the day's boundaries. The Jewish day begins at either sunset or at nightfall (when three second-magnitude stars appear). Medieval Europe followed this tradition, known as Florentine reckoning: in this system, a reference like "two hours into the day" meant two hours after sunset and thus times during the evening need to be shifted back one calendar day in modern reckoning. Days such as Christmas Eve, Halloween, and the Eve of Saint Agnes are the remnants of the older pattern when holidays began the evening before. Present common convention is for the civil day to begin at midnight, that is 00:00, and last a full twenty-four hours until the next 00:00 (also known as 24:00, but this is not as widely used). In ancient Egypt the day was reckoned from sunrise to sunrise. Muslims fast from dawn (traditionally when a white thread can be distinguished from a black thread) to sunset each day of the month of Ramadan. In the United States, nights are named after the previous day, e.g. "Friday night" usually means the entire night between Friday and Saturday. This is the opposite of the Jewish pattern. This difference from the civil day often leads to confusion. Events starting at midnight are often announced as occurring the day before. TV-guides tend to list nightly programs at the previous day, although programming a VCR requires the strict logic of starting the new day at 00:00 (to further confuse the issue, VCRs set to the 12-hour clock notation will label this "12:00 AM"). Expressions like "today", "yesterday" and "tomorrow" become ambiguous during the night. Validity of tickets, passes, etc., for a day or a number of days may end at midnight, or closing time, when that is earlier. However, if a service (e.g. public transport) operates from e.g. 6:00 to 1:00, the last hour may well count as being part of the previous day (also for the arrangement of the timetable). For services depending on the day ("closed on Sundays", "does not run on Fridays", etc.) there is a risk of ambiguity. As an example, for the Dutch Railways, a day ticket is valid 28 hours, from 0:00 to 4:00 the next night.

List of famous days

- Black Monday
- Black Friday
- Bloody Sunday
- D-Day
- The Day The Music Died
- Ides of March
- Judgement Day
- September 11, 2001 See also List of commemorative days

People named Day

Some noted people with the name Day include Doris Day, Stockwell Day, and Dorothy Day.

External links

- [http://www.fourmilab.ch/cgi-bin/uncgi/Earth/action?opt=-p&img=learth.evif Show where it is daytime at the moment]
- [http://ptaff.ca/soleil/?lang=en_CA Sunrise and sunset, all year long, anywhere] Category:Units of time als:Tag ko:일 (시간) ja:日 simple:Day th:วัน

Greenwich Mean Time

Greenwich Mean Time (GMT) is mean solar time at the Royal Greenwich Observatory in Greenwich, London, England, which by convention is at 0 degrees geographic longitude. Noon Greenwich Mean Time is not the moment when the Sun crosses the Greenwich meridian (and reaches its highest point in the sky in Greenwich) because of Earth's uneven speed in its elliptic orbit and its axial tilt. This event may be up to 16 minutes away from noon GMT (this discrepancy is known as the equation of time). The fictitious mean sun is the annual average of this nonuniform motion of the true Sun, necessitating the inclusion of mean in Greenwich Mean Time. equation of time, green - Eastern European Time, khaki - Moscow Time.]] As Great Britain grew into an advanced maritime nation, English mariners kept their timepieces on GMT in order to calculate their longitude "from the Greenwich meridian". This did not affect shipboard time itself, which was still solar time. This combined with mariners from other nations drawing from Nevil Maskelyne's method of lunar distances based on observations at Greenwich, eventually led to GMT being used world-wide as a reference time independent of location. Most time zones were based upon this reference as a number of hours and half-hours "ahead of GMT" or "behind GMT". Hourly time signals from Greenwich Observatory were first broadcast on 5 February 1924. The daily rotation of the Earth is somewhat irregular (see ΔT) and is slowing down slightly. Atomic clocks represent a much more stable timebase. On 1 January 1972, GMT was replaced as the international time reference by Coordinated Universal Time (UTC), maintained by an ensemble of atomic clocks around the world. UT1 was introduced to represent "earth rotation time". Leap seconds are added to or subtracted from UTC to keep it within 0.9 seconds of UT1. Although civil time, e.g., the Greenwich Time Signal in Great Britain, is now based on UTC, it is still popularly called GMT. It is also called Western European Time (WET). Those countries marked in dark blue on the map at right use European Summer Time and advance their clock one hour in summer. In Great Britain, this is known as British Summer Time (BST); in Ireland it is called Irish Summer Time (IST). Those countries marked in light blue keep their clocks on UTC/GMT/WET year round.

External Links

- [http://wwp.greenwichmeantime.com Greenwich Mean Time]
- [http://physics.nist.gov/GenInt/Time/world.html NIST - World Time Scales]
- [http://hpiers.obspm.fr/ International Earth Rotation and Reference Systems Service] Category:Time scales Category:Greenwich ko:그리니치 평균시 ja:グリニッジ標準時

January 1

January 1 is the first day of the calendar year in both the Julian and Gregorian calendars. Here a calendar year refers to the order in which the months are displayed, January to December. The first day of the medieval Julian year was usually a day other than January 1. This day was adopted as the first day of the Julian year by all Western European countries except England between about 1450 and 1600. The Gregorian calendar as promulgated in 1582 did not specify that January 1 was to be either New Year's Day or the first day of its numbered year. Although England began its numbered year on March 25 (Lady Day or Annunciation Day), between the 13th century and 1752, January 1 was called New Year's Day, and was, with Christmas and occasionally Twelfth Night, a holiday when gifts were exchanged. 364 days (365 in leap years) remain in the year after this day.

Events

- 45 BC - The Julian calendar first takes effect.
- 404 - Last known gladiator competition in Rome takes place.
- 630 - Prophet Muhammad sets out toward Mecca with the army that will capture it bloodlessly.
- 990 - Kievan Rus' adopts the Julian calendar.
- 1438 - Albert II of Habsburg is crowned King of Hungary.
- 1600 - Scotland begins using the Julian calendar.
- 1651 - Charles II crowned King of Scotland
- 1673 - Regular mail delivery begins between New York and Boston.
- 1700 - Russia begins using the Julian calendar.
- 1707 - John V is crowned King of Portugal
- 1738 - Bouvet Island is discovered by French explorer Jean-Baptiste Charles Bouvet de Lozier.
- 1788 - First edition of The Times of London, previously The Daily Universal Register, is published.
- 1797 - Albany replaces New York City as the capital on New York.
- 1801 - Legislative union of Kingdom of Great Britain and Kingdom of Ireland is completed to form United Kingdom.
- 1801 - The first known asteroid, 1 Ceres, is discovered by Giuseppe Piazzi.
- 1804 - French rule ends in Haiti.
- 1808 - Importation of slaves into the United States is banned.
- 1818 - Mary Shelley's novel Frankenstein, or The Modern Prometheus is published.
- 1855 - London, Ontario is incorporated as a city.
- 1861 - Porfirio Diaz conquers Mexico City.
- 1863 - American Civil War: The Emancipation Proclamation takes effect.
- 1863 - The first claim under the Homestead Act is made by Daniel Freeman for a farm in Nebraska.
- 1880 - Ferdinand de Lesseps begins French construction of the Panama Canal.
- 1887 - Queen Victoria was proclaimed empress of India in Delhi.
- 1892 - Ellis Island opens to begin accepting immigrants to the United States.
- 1893 - Japan begins using the Gregorian calendar.
- 1894 - The Manchester Ship Canal, England, was officially opened to traffic.
- 1898 - New York City annexes land from surrounding counties, creating the City of Greater New York. The four initial boroughs, Manhattan, Brooklyn, Queens, and The Bronx, are joined on January 25th by Staten Island to create the modern city of five boroughs.
- 1899 - Spanish rule ends in Cuba.
- 1901 - Nigeria becomes a British protectorate.
- 1901 - The British colonies of New South Wales, Queensland, Victoria, South Australia and Western Australia federate as the Commonwealth of Australia; Edmund Barton becomes first Prime Minister.
- 1901 - The first official Mummers Parade is held.
- 1902 - The first Rose Bowl game is played in Pasadena, California.
- 1908 - For the first time, a ball is dropped in New York City's Times Square to signify the start of the New Year.
- 1911 - Northern Territory is separated from South Australia and transferred to Commonwealth control.
- 1912 - The Republic of China is established.
- 1916 - German troops abandon Yaoundé and their Kamerun colony to British forces and begin the long march to Spanish Guinea.
- 1934 - Alcatraz Island becomes a U.S. federal prison.
- 1934 - Nazi Germany passes the "Law for the Prevention of Genetically Diseased Offspring".
- 1935 - Bucknell University wins the first Orange Bowl 26-0 over the University of Miami.
- 1937 - Anastasio Somoza becomes President of Nicaragua.
- 1937 - The first Cotton Bowl game is played in Dallas, Texas.
- 1939 - The Vienna New Year's Concert is first held.
- 1942 - The Declaration by the United Nations is signed by twenty-six nations.
- 1948 - British railways are nationalised to form British Rail.
- 1948 - After partition, India declines to pay the agreed share of Rs.550 million in cash balances to Pakistan.
- 1948 - Enrico De Nicola formally becomes President of the Italian Republic, but refuses to be a candidate for the first constitutional election the following May.
- 1949 - UN Cease-fire orders to operate in Kashmir from one minute before midnight. War between India and Pakistan stops accordingly.
- 1956 - The Republic of the Sudan achieves independence from the Egyptian Republic and the United Kingdom of Great Britain and Northern Ireland.
- 1958 - The European Community is established.
- 1959 - Fulgencio Batista, President of the Republic of Cuba, is overthrown by Fidel Castro's forces.
- 1960 - The Republic of Cameroon achieves independence from France and the United Kingdom of Great Britain and Northern Ireland.
- 1962 - Western Samoa achieves independence from New Zealand; its name is changed to the Independent State of Western Samoa.
- 1964 - The Federation of Rhodesia and Nyasaland is divided into the independent republics of Zambia and Malawi, and the British-controlled Rhodesia.
- 1969 - Marien Ngouabi formally becomes the President of the Republic of Congo.
- 1970 - The Unix epoch begins at 00:00:00 UTC.
- 1971 - Cigarette advertisements are banned on American television.
- 1973 - The Kingdom of Denmark, the United Kingdom of Great Britain and Northern Ireland, and the Republic of Ireland are admitted into the European Community.
- 1976 - NBC introduces its new logo: an abstract N, similar to the Nebraska Educational Television Network logo.
- 1978 - Air India Flight 855 Boeing 747 explodes and crashes into the sea off the coast of Bombay, killing 213.
- 1979 - Formal diplomatic relations are established between the People's Republic of China and the United States of America.
- 1981 - The Republic of Greece is admitted into the European Community.
- 1981 - The Republic of Palau achieves self-government; it is not yet independent from the United States of America.
- 1983 - The ARPANET officially changes to using the Internet Protocol, creating the Internet.
- 1984 - AT&T is broken up into twenty-two independent units.
- 1984 - The Sultanate of Brunei becomes independent of the United Kingdom of Great Britain and Northern Ireland.
- 1985 - The Internet's Domain Name System is created.
- 1985 - The first British mobile phone call is made by Ernie Wise to Vodafone.
- 1986 - Aruba becomes independent of Curaçao, though it remains in free association with the Kingdom of the Netherlands.
- 1986 - Spain and Portugal are admitted into the European Community.
- 1988 - The Evangelical Lutheran Church in America comes into existence, creating the largest Lutheran denomination in the United States of America.
- 1993 - Velvet Divorce: Czechoslovakia is divided into the Slovak Republic and the Czech Republic.
- 1993 - A single market within the European Community is introduced.
- 1993 - Pakistan is elected member of the 15-nation UN Security Council.
- 1994 - The Zapatista Army of National Liberation initiates twelve days of armed conflict in the Mexican State of Chiapas.
- 1994 - The North American Free Trade Agreement comes into effect.
- 1995 - The World Trade Organization comes into effect.
- 1995 - The Kingdom of Sweden and the republics of Austria and Finland are admitted into the European Union.
- 1995 - The Conference for Security and Co-operation in Europe becomes the Organization for Security and Co-operation in Europe.
- 1996 - Curaçao gains limited self-government, though it remains within free association with the Kingdom of the Netherlands.
- 1997 - The Republic of Zaïre officially joins the World Trade Organization, as Zaïre.
- 1998 - Smoking is banned in all bars and restaurants in the State of California.
- 1999 - The Euro currency is introduced.
- 2002 - Euro banknotes and coins become legal tender in twelve of the European Union's member states.
- 2002 - The Republic of China officially joins the World Trade Organization, as Chinese Taipei.
- 2002 - The Open Skies mutual surveillance treaty, initially signed in 1992, officially enters into force.
- 2003 - Luís Inácio Lula da Silva becomes president of the Federative Republic of Brazil.
- 2004 - Pervez Musharraf receives a vote of confidence to continue as the President of the Islamic Republic of Pakistan from Parliament and the provincial assemblies.

Births

- 766 - Ali ar-Rida, Shia Imam (d. 818)
- 1431 - Pope Alexander VI (d. 1503)
- 1449 - Lorenzo de Medici, Italian statesman (d. 1492)
- 1484 - Huldrych Zwingli, Swiss Protestant leader (d. 1531)
- 1516 - Margareta Leijonhufvud, queen of Gustav I of Sweden (d. 1551)
- 1557 - Stephen Bocskay, Prince of Transylvania (d. 1606)
- 1600 - Friedrich Spanheim, Dutch theologian (d. 1649)
- 1614 - John Wilkins, English Bishop of Chester (d. 1672)
- 1618 - Bartolomé Esteban Murillo, Spanish painter (d. 1682)
- 1638 - Emperor Go-Sai of Japan (d. 1685)
- 1648 - Elkanah Settle, English writer (d. 1724)
- 1655 - Christian Thomasius, German jurist (d. 1728)
- 1684 - Arnold Drakenborch, Dutch classical scholar (d. 1748)
- 1704 - Soame Jenyns, English writer (d. 1787)
- 1711 - Franz Freiherr von der Trenck, Austrian soldier (d. 1749)
- 1714 - Kristijonas Donelaitis, Lithuanian poet (d. 1780)
- 1735 - Paul Revere, American silversmith and patriot (d. 1818)
- 1750 - Frederick Muhlenberg, first speaker of the United States House of Representatives (d. 1801)
- 1752 - Betsy Ross, American seamstress (d. 1836)
- 1774 - André Marie Constant Duméril, French zoologist (d. 1860)
- 1793 - Francesco Guardi, Italian artist (b. 1712)
- 1823 - Sándor Petőfi, Hungarian poet and revolutionary (d. 1849)
- 1833 - Robert Lawson, New Zealand architect (d. 1902)
- 1839 - Ouida, English writer (d. 1908)
- 1854 - Sir James George Frazer, Scottish anthropologist (d. 1941)
- 1860 - George Washington Carver, American educator, inventor, and botanist (d. 1943)
- 1863 - Pierre de Coubertin, French initiator of the modern Olympic Games (d. 1937)
- 1864 - Alfred Stieglitz, American photographer (d. 1946)
- 1873 - Mariano Azuela, Mexican novelist (d. 1952)
- 1874 - Gustave Whitehead, German-American inventor (d. 1927)
- 1876 - Harriet Brooks, Canadian physicist (d. 1933)
- 1879 - E. M. Forster, English novelist (d. 1970)
- 1887 - Wilhelm Canaris, German admiral (d. 1945)
- 1890 - Anton Melik, Slovenian geographer (d. 1966)
- 1892 - Artur Rodzinski, Croatian conductor (d. 1958)
- 1894 - Satyendra Nath Bose, Indian mathematician (d. 1974)
- 1895 - J. Edgar Hoover, American Federal Bureau of Investigation director (d. 1972)
- 1900 - Xavier Cugat, Catalan-Cuban musician, bandleader (d. 1990)
- 1902 - Buster Nupen, South African cricketer (d. 1977)
- 1904 - Fazal Ilahi Chaudhry, Pakistani politician (d. 1982)
- 1906 - Giovanni D'Anzi, Italian songwriter (d. 1974)
- 1909 - Dana Andrews, American actor (d. 1992)
- 1909 - Barry M. Goldwater, U.S. Senator from Arizona and Presidential candidate (d. 1998)
- 1911 - Hank Greenberg, baseball player (d. 1986)
- 1912 - Kim Philby, British spy (d. 1988)
- 1917 - Jule Gregory Charney, meteorologist (d. 1981)
- 1917 - Albert Mol, Dutch actor (d. 2004)
- 1919 - J. D. Salinger, American novelist
- 1920 - Virgilio Savona, Italian singer and songwriter (Quartetto Cetra)
- 1921 - Isma'il Raji' al-Faruqi, Palestinian-born philosopher and comparative religion scholar (d. 1986)
- 1922 - Rocky Graziano, American boxer (d. 1990)
- 1925 - Stymie Beard, American actor (d. 1981)
- 1927 - Vernon L. Smith, American economist, Nobel Prize laureate
- 1927 - Doak Walker, American football star (d 1998)
- 1928 - Ernest Tidyman, American writer (d. 1984)
- 1933 - Frederick Lowy, Canadian medical educator, ethicist, and university president
- 1933 - Joe Orton, English writer (d. 1967)
- 1940 - Frank Langella American actor
- 1942 - Martin Frost, American politician
- 1942 - Country Joe McDonald, American musician (Country Joe and the Fish)
- 1942 - Gennadi Sarafanov, cosmonaut
- 1943 - Don Novello, American actor, comedian, and writer
- 1945 - Jacky Ickx, Belgian race car driver
- 1946 - Rivelino, Brazilian football player
- 1953 - Greg Carmichael, British guitarist
- 1957 - Luis Guzmán, Puerto Rican actor
- 1958 - Grandmaster Flash, West Indian-born singer
- 1959 - Azali Assoumani, Comorese president
- 1961 - Mark Wingett, British actor
- 1964 - Dedee Pfeiffer, American actress
- 1966 - Embeth Davidtz, American actress
- 1968 - Davor Šuker, Croatian footballer
- 1969 - Verne Troyer - American actor
- 1970 - Gabriel Jarret, American actor
- 1972 - Neve McIntosh, Scottish actress
- 1975 - Joe Cannon, American soccer player
- 1977 - Hasan Salihamidžić, Bosnian footballer
- 1978 - Erica Durance, Canadian actress
- 1978 - Jared Fogle, American calibate
- 1978 - Paramahamsa Sri Nithyananda, Indian spiritual guru
- 1978 - Nina Bott, German actress
- 1979 - Brody Dalle, Australian singer (The Distillers)
- 1979 - Koichi Domoto, Japanese artist
- 1980 - Elin Nordegren, Swedish model
- 1981 - Zsolt Baumgartner, Hungarian race car driver
- 1981 - Abdulkadir Kocak, Turkish boxer
- 1982 - David Nalbandian, Argentinian tennis player
- 1985 - Steve Davis, Irish footballer

Deaths

- 379 - Saint Basil of Caesarea (b. 330)
- 404 - Saint Telemachus
- 874 - Hasan al-Askari, eleventh Shia Imam (b. 846)
- 898 - Odo, Count of Paris (b. 860)
- 1204 - King Haakon III of Norway
- 1384 - King Charles II of Navarre (b. 1332)
- 1515 - King Louis XII of France (b. 1462)
- 1554 - Pedro de Valdivia, Spanish conquistador
- 1559 - Christian III of Denmark and Norway (b. 1503)
- 1560 - Joachim Du Bellay, French poet
- 1617 - Hendrik Goltzius, Dutch painter (b. 1558)
- 1679 - Jan Steen, Dutch painter
- 1716 - William Wycherley, English dramatist
- 1730 - Samuel Sewall, English-born judge (b. 1652)
- 1742 - Peregrine Bertie, 2nd Duke of Ancaster and Kesteven, English statesman (b. 1686)
- 1748 - Johann Bernoulli, Swiss mathematician (b. 1667)
- 1766 - James Francis Edward Stuart, "The Old Pretender" (b. 1688)
- 1782 - Johann Christian Bach, German composer (b. 1735)
- 1789 - Fletcher Norton, 1st Baron Grantley, English politician (b. 1716)
- 1793 - Francesco Guardi, Venetian painter (b. 1712)
- 1800 - Louis-Jean-Marie Daubenton, French naturalist (b. 1716)
- 1817 - Martin Heinrich Klaproth, German chemist (b. 1743)
- 1892 - Roswell B. Mason, Mayor of Chicago (b. 1805)
- 1894 - Heinrich Hertz, German physicist (b. 1857)
- 1933 - Harriet Brooks, Canadian physicist (b. 1876)
- 1944 - Charles Turner, Australian cricketer (b. 1862)
- 1953 - Hank Williams, American singer (b. 1923)
- 1958 - Edward Weston, American photographer (b. 1886)
- 1960 - Margaret Sullavan, American actress (b. 1911)
- 1964 - Bechara El Khoury, President of Lebanon (b. 1890)
- 1972 - Maurice Chevalier, French actor and singer (b. 1888)
- 1981 - Beulah Bondi, American actress (b. 1888)
- 1986 - Alfredo Binda, Italian cyclist (b. 1902)
- 1992 - Grace Hopper, American computer pioneer (b. 1906)
- 1994 - Lord Arthur Espie Porritt, Governor-General of New Zealand (b. 1900)
- 1994 - Cesar Romero, American actor (b. 1907)
- 1995 - Fred West, British serial killer (suicide) (b. 1941)
- 1995 - Eugene Wigner, Hungarian physicist, Nobel Prize laureate (b. 1902)
- 1996 - Arleigh Burke, U.S. admiral (b. 1901)
- 1997 - Townes Van Zandt, American musician (b. 1944)
- 1998 - Helen Wills Moody, American tennis player (b. 1905)
- 2001 - Ray Walston, American actor (b. 1914)
- 2003 - Joe Foss, American politician and fighter pilot (b. 1915)
- 2005 - Shirley Chisholm, first black U.S. Congresswoman (b. 1924)
- 2005 - Hugh John Frederick Lawson, 6th Baron Burnham, British newspaperman and politician (b. 1931)
- 2005 - Bob Matsui, U.S. Congressman (b. 1941)

Holidays and observances

- The seventh day and eighth night of Christmas in Western Christianity.
- Many countries around the world using Gregorian Calendar - New Year's Day; often celebrated at 0:00 with fireworks.
- Catholicism - Holy Day of Obligation Octave of Christmas, Blessed Virgin Mary, Mother of God (New calendar).
- Catholicism - Feast of the Circumcision (Old calendar).
- Catholicism - National Migration Week begins (varying official support by the office of U.S. President, not strictly religious)
- Haiti Independence Day
- Taiwan Founding of Republic of China.
- Sudan Independence Day
- Cuba Liberation Day
- Slovakia: Establishment of Slovak Republic.
- Last day of Kwanzaa
- Vienna New Year's Concert
- Pasadena, California - The Tournament of Roses parade and, traditionally, the Rose Bowl football championship
- World Day for Prayer for Peace

External links

- [http://news.bbc.co.uk/onthisday/hi/dates/stories/january/1 BBC: On This Day] ---- December 31 - January 2 - December 1 - February 1 — listing of all days ko:1월 1일 ms:1 Januari ja:1月1日 simple:January 1 th:1 มกราคม

5th millennium BC

__NOTOC__ (6th millennium BC – 5th millennium BC – 4th millennium BC – other millennia)

Events

- 4860 BC - Mount Mazama in Oregon collapses, forming a caldera that later fills with water and becomes Crater Lake, the deepest lake in the United States.
- 4713 BC – The epoch (origin) of the Julian Period described by Joseph Justus Scaliger occurred on January 1, the astronomical Julian day number zero.
- 4004 BC – The universe is created at nightfall preceding October 23 according to the Ussher-Lightfoot chronology of Archbishop James Ussher of Armagh.

Cultures

- c. 4800 - 4600 BC; arrangements of circular ditches are built in Central Europe
- c. 4500 BC – Civilization of Susa and Kish in Mesopotamia and Khuzestan (see Sialk)
- Cucuteni culture
- the chalcolithic Sredny Stog, Samara and early Maykop cultures, candidates for the early Proto-Indo-Europeans

Periods

- c. 4570–4250 BC – Merimde culture on the Nile
- c. 4400–4000 BC – Badari culture on the Nile

Inventions, discoveries, introductions

- from ca. 5000 BC: development of proto-writing systems, possibly ideographic: Vinca script, Tartaria tablets.
- ca. 4500 BC – Introduction of the plough in Europe
- Domestication of the Water Buffalo in China
- Development of beer-making ja:紀元前5千年紀

International Astronomical Union

The International Astronomical Union (IAU) unites national astronomical societies from around the world. It is a member of the International Council of Science (ICSU). It is the most popularly recognised authority for the naming of stars, planets, asteroids and other celestial bodies and phenomena in the scientific community. Working groups include the Working Group for Planetary System Nomenclature (WGPSN), which maintains the astronomical naming conventions and planetary nomenclature for planetary bodies. The IAU is also responsible for the system of Astronomical Telegrams, although it does not run it. The Minor Planet Center (MPC), a clearinghouse for all non-planetary or non-moon bodies in the solar system, also operates under the IAU. The IAU was founded in 1919, as a merger of various international projects including the Carte du Ciel, the Solar Union and the International Time Bureau (Bureau International de l'Heure). The first president was Benjamin Baillaud. The IAU currently has 9040 individual members, i.e., professional astronomers (mainly) at the PhD level; and 63 national members, i.e., countries that are affiliated with the IAU. 87 percent of all members are male; 13 percent are female. The current president is Ronald D. Ekers. The [http://www.astronomy2006.com XXVIth General Assembly] of the International Astronomical Union (August 2006) will be held in Prague, Czech Republic.

In pop culture

- In the song "Planet X" by Christine Lavin, there are lyrics referring to both the IAU and WGPSN.
- In the movie Deep Impact, the actual scientific group to which the amateur would report the finding of a new asteroid would be the MPC.

External link

- [http://www.iau.org/ Website of the International Astronomical Union]
- [http://www.astronomy2006.com XXVIth General Assembly 2006] Category:Standards organizations Category:Astronomy organizations ja:国際天文学連合 th:สหพันธ์ดาราศาสตร์สากล

Julian calendar

The Julian calendar was introduced in 46 BC by Julius Caesar and took force in 45 BC (709 ab urbe condita). It was chosen after consultation with the Alexandrian astronomer Sosigenes and was probably designed to approximate the tropical year, known at least since Hipparchus. It has a regular year of 365 days divided into 12 months, and a leap day is added to February every four years. Hence the Julian year is on average 365.25 days long. The Julian calendar remained in use into the 20th century in some countries and is still used by many national Orthodox churches. However, too many leap days are added with respect to the astronomical seasons on this scheme. On average, the astronomical solstices and the equinoxes advance by about 11 minutes per year against the Julian year, causing the calendar to gain a day about every 134 years. While Hipparchus and presumably Sosigenes were aware of the discrepancy, although not of its correct value, it was evidently felt to be of little importance. However, it accumulated significantly over time, and eventually led to the reform of 1582, which replaced the Julian calendar with the more accurate Gregorian calendar. The notation "Old Style" (OS) is sometimes used to indicate a date in the Julian calendar, as opposed to "New Style", which indicates a date in the Gregorian Calendar. This notation is used when there might otherwise be confusion about which date is found in a text.

From Roman to Julian

The ordinary year in the previous Roman calendar consisted of 12 months, for a total of 355 days. In addition, an intercalary month, the Mensis Intercalaris, was sometimes inserted between February and March. This intercalary month was formed by inserting 22 days before the last five days of February, creating a 27-day month. It began after a truncated February having 23 or 24 days, so that it had the effect of adding 22 or 23 days to the year, forming an intercalary year of 377 or 378 days. According to the later writers Censorinus and Macrobius, the ideal intercalary cycle consisted of ordinary years of 355 days alternating with intercalary years, which were alternately 377 and 378 days long. On this system, the average Roman year would have had 366¼ days over four years, giving it an average drift of one day per year relative to any solstice or equinox. Macrobius describes a further refinement wherein, for 8 years out of 24, there were only three intercalary years each of 377 days. This refinement averages the length of the year to 365¼ days over 24 years. In practice, intercalations did not occur schematically according to these ideal systems, but were determined by the pontifices. So far as can be determined from the historical evidence, they were much less regular than these ideal schemes suggest. They usually occurred every second or third year, but were sometimes omitted for much longer, and occasionally occurred in two consecutive years. If managed correctly this system allowed the Roman year, on average, to stay roughly aligned to a tropical year. However, if too many intercalations were omitted, as happened after the Second Punic War and during the Civil Wars, the calendar would drift rapidly out of alignment with the tropical year. Moreover, since intercalations were often determined quite late, the average Roman citizen often did not know the date, particularly if he were some distance from the city. For these reasons, the last years of the pre-Julian calendar were later known as years of confusion. The problems became particularly acute during Julius Caesar's pontificate, 63 BC to 46 BC, when there were only five intercalary months, whereas there should have been eight, and none at all during the five Roman years before 46 BC. The Julian reform was intended to correct this problem permanently. Before it took effect, the missed intercalations during Julius Caesar's pontificate were made up by inserting 67 days (22+23+22) between November and December of 46 BC in the form of two months, in addition to 23 days which had already been added to February. Thus 90 days were added to this last year of the Roman Republican calendar, giving it 445 days. Because it was the last of a series of irregular years, this extra-long year was, and is, referred to as the last year of confusion. The first year of operation of the new calendar was 45 BC.

Leap years error

Despite the new calendar being much simpler than the Roman calendar, the pontifices apparently misunderstood the algorithm. They added a leap day every three years, instead of every four years. According to Macrobius, the error was the result of counting inclusively, so that the four year cycle was considered as including both the first and fourth years. This resulted in too many leap days. Caesar Augustus remedied this discrepancy by restoring the correct frequency after 36 years of this mistake. He also skipped several leap days in order to realign the year. The historic sequence of leap years (i.e. years with a leap day) in this period is not given explicitly by any ancient source, although the existence of the triennial leap year cycle is confirmed by an inscription that dates from 9 or 8 BC. The chronologist Joseph Scaliger established in 1583 that the Augustan reform was instituted in 8 BC, and inferred that the sequence of leap years was 42, 39, 36, 33, 30, 27, 24, 21, 18, 15, 12, 9 BC, AD 8, 12 etc. This proposal is still the most widely accepted solution. It has also sometimes been suggested that 45 BC was a leap year. Other solutions have been proposed from time to time. Kepler proposed in 1614 that the correct sequence of leap years was 43, 40, 37, 34, 31, 28, 25, 22, 19, 16, 13, 10 BC, AD 8, 12 etc. In 1883 the German chronologist Matzat proposed 44, 41, 38, 35, 32, 29, 26, 23, 20, 17, 14, 11 BC, AD 4, 8, 12 etc., based on a passage in Dio Cassius that mentions a leap day in 41 BC that was said to be contrary to (Caesar's) rule. In the 1960s Radke argued the reform was actually instituted when Augustus became pontifex maximus in 12 BC, suggesting the sequence 45, 42, 39, 36, 33, 30, 27, 24, 21, 18, 15, 12 BC, AD 4, 8, 12 etc. In 1999, an Egyptian papyrus was published which gives an ephemeris table for 24 BC with both Roman and Egyptian dates. From this it can be shown that the most likely sequence was in fact 44, 41, 38, 35, 32, 29, 26, 23, 20, 17, 14, 11, 8 BC, AD 4, 8, 12 etc, very close to that proposed by Matzat. This sequence shows that the standard Julian leap year sequence began in AD 4, the twelfth year of the Augustan reform. Also, under this sequence the actual Roman year coincided with the proleptic Julian year between 32 and 26 BC. This suggests that one aim of the realignment portion of the Augustan reform was to ensure that key dates of his career, notably the fall of Alexandria on 1 August 30 BC, were unaffected by his correction. Roman dates before 32 BC were typically a day or two before the day with the same Julian date, so 1 January in the Roman calendar of the first year of the Julian reform actually fell on 31 December 46 BC (Julian date). A curious effect of this is that Caesar's assassination on the Ides (15th day) of March in 44 BC fell on 14 March 44 BC in the Julian calendar.

Naming of the months

Immediately after the Julian reform, the twelve months of the Roman calendar were named Ianuarius, Februarius, Martius, Aprilis, Maius, Iunius, Quintilis, Sextilis, September, October, November, and December, just as they were before the reform. Their lengths were set to their modern values. The old intercalary month, the Mensis Intercalaris, was abolished and replaced with an single intercalary day at the same point (i.e. five days before the end of Februarius). The first month of the year continued to be Ianuarius, as it had been since 153 BC. The Romans later renamed months after Caesar and Augustus, renaming Quintilis (originally, "the Fifth month", with March = month 1) as Iulius (July) in 44 BC and Sextilis ("Sixth month") as Augustus (August) in 8 BC. (Note that the letter J was not invented until the 17th century). Quintilis was renamed to honour Caesar because it was the month of his birth. According to a senatusconsultum quoted by Macrobius, Sextilis was renamed to honour Augustus because several of the most significant events in his rise to power, culminating in the fall of Alexandria, fell in that month. Other months were renamed by other emperors, but apparently none of the later changes survived their deaths. Caligula renamed September ("Seventh month") as Germanicus; Nero renamed Aprilis (April) as Neroneus, Maius (May) as Claudius and Iunius (June) as Germanicus; and Domitian renamed September as Germanicus and October ("Eighth month") as Domitianus. At other times, September was also renamed as Antoninus and Tacitus, and November ("Ninth month") was renamed Faustina and Romanus. Commodus was unique in renaming all twelve months after his own adopted names (January to December): Amazonius, Invictus, Felix, Pius, Lucius, Aelius, Aurelius, Commodus, Augustus, Herculeus, Romanus, and Exsuperatorius. Much more lasting than the ephemeral month names of the post-Augustan Roman emperors were the names introduced by Charlemagne. He renamed all of the months agriculturally into Old High German. They were used until the 15th century, and with some modifications until the late 18th century in Germany and in the Netherlands (January-December): Wintarmanoth (winter month), Hornung (spring), Lentzinmanoth (Lent month), Ostarmanoth (Easter month), Winnemanoth (grazing month), Brachmanoth (plowing month), Heuvimanoth (hay month), Aranmanoth (harvest month), Witumanoth (wood month), Windumemanoth (vintage month), Herbistmanoth (autumn/harvest month), and Heilagmanoth (holy month). Translations of these month names are still used to this day in some Slavic languages, such as Polish.

Lengths of the months

According to the 13th century scholar Sacrobosco, the original scheme for the months in the Julian Calendar was very regular, alternately long and short. From January through December, the month lengths according to Sacrobosco for the Roman Republican calendar were: :30, 29, 30, 29, 30, 29, 30, 29, 30, 29, 30, and 29, totaling 354 days. He then thought that Julius Caesar added one day to every month except February, a total of 11 more days, giving the year 365 days. A leap day could now be added to the extra short February: :31, 29 (30), 31, 30, 31, 30, 31, 30, 31, 30, 31, and 30 He then said Augustus changed this to: :31, 28 (29), 31, 30, 31, 30, 31, 31, 30, 31, 30, and 31 giving us the irregular month lengths which we still use today, so that the length of Augustus would not be shorter than (and therefore inferior to) the length of Iulius. Although this theory is still widely repeated, it is certainly wrong. First, a wall painting of a Roman Republican calendar has survived [http://www.personal.psu.edu/users/w/x/wxk116/RomanCalendar/Fasti4.gif] which confirms the literary accounts that the months were already irregular before Julius Caesar reformed it: :29, 28, 31, 29, 31, 29, 31, 29, 29, 31, 29, and 29 Also, the Julian reform did not change the dates of the Nones and Ides. In particular, the Ides are late (on the 15th rather than 13th) in March, May, July and October, showing that these months always had 31 days in the Roman calendar, whereas Sacrobosco's theory requires that the length of October was changed. Further, Sacrobosco's theory is explicitly contradicted by the third and fifth century authors Censorinus and Macrobius, and, finally, it is inconsistent with seasonal lengths given by Varro, writing in 37 BC, before the Augustan reform, with the 31-day Sextilis given by the new Egyptian papyrus from 24 BC, and with the 28-day February shown in the Fasti Caeretani, which is dated before 12 BC.

Year numbering

The dominant method that the Romans used to identify a year for dating purposes was to name it after the two consuls who took office in it. Since 153 BC, they had taken office on 1 January, and Julius Caesar did not change the beginning of the year. Thus this consular year was an eponymous or named year. Roman years were named this way until the last consul was appointed in 541. Only rarely did the Romans number the year from the founding of the city (of Rome), ab urbe condita (AUC). This method was used by Roman historians to determine the number of years from one event to another, not to date a year. Different historians had several different dates for the founding. The Fasti Capitolini, an inscription containing an official list of the consuls which was published by Augustus, used an epoch of 752 BC. The epoch used by Varro, 753 BC, has been adopted by modern historians. Indeed, Renaissance editors often added it to the manuscripts that they published, giving the false impression that the Romans numbered their years. Most modern historians tacitly assume that it began on the day the consuls took office, and ancient documents such as the Fasti Capitolini which use other AUC systems do so in the same way. However, the Varronian AUC year did not formally begin on 1 January, but on Founder's Day, 21 April. This prevented the early Roman church from celebrating Easter after 21 April because the festivities associated with Founder's Day conflicted with the solemnity of Lent, which was observed until the Saturday before Easter Sunday. In addition to consular years, the Romans sometimes used the regnal year of the emperor. Anno Diocletiani, named after Diocletian, was often used by the Alexandrian Christians to number their Easters during the fourth and fifth centuries. In AD 537, Justinian required that henceforth the date must include the name of the emperor, in addition to the indiction and the consul (the latter ending only four years later). The indiction caused the Byzantine year to begin on 1 September, which is still used in the Eastern Orthodox Church for the beginning of the liturgical year. In AD 525 Dionysius Exiguus proposed the system of anno Domini, which gradually spread through the western Christian world, once the system was adopted by Bede. Years were numbered from the supposed date of the incarnation or annunciation of Jesus on 25 March, although this soon changed to Christmas, then back to Annunciation Day in Britain, and the numbered year even began on Easter in France.

From Julian to Gregorian

The Julian calendar was in general use in Europe from the times of the Roman Empire until 1582, when Pope Gregory XIII promulgated the Gregorian Calendar, which was soon adopted by most Catholic countries. The Protestant countries followed later, and the countries of Eastern Europe even later. Great Britain had Thursday 14 September 1752 follow Wednesday 2 September 1752. Sweden adopted the new style calendar in 1753, but also for a twelve-year period starting in 1700 used a modified Julian Calendar. Russia remained on the Julian calendar until after the Russian Revolution (which is thus called the 'October Revolution' but occurred in November according to the Gregorian calendar), in 1917, while Greece continued to use it until 1923. Although all Eastern European countries had adopted the Gregorian calendar on or before 1923, their national Eastern Orthodox churches had not. A revised Julian calendar was proposed during a synod in Constantinople in May of 1923, consisting of a solar part which was and will be identical to the Gregorian calendar until the year 2800, and a lunar part which calculated Easter astronomically at Jerusalem. All Orthodox churches refused to accept the lunar part, so almost all Orthodox churches continue to celebrate Easter according to the Julian calendar (the Finnish Orthodox Church uses the Gregorian Easter). The solar part was only accepted by some Orthodox churches, those of Constantinople, Alexandria, Antioch, Greece, Cyprus, Romania, Poland, Bulgaria (in 1963), and the Orthodox Church in America (although some OCA parishes are permitted to use the Julian calendar). Thus, these churches celebrate the Nativity on the same day that Western Christians do, 25 December Gregorian until 2800. The Orthodox churches of Jerusalem, Russia, Serbia, Georgia, Ukraine, and the Greek Old Calendarists continue to use the Julian calendar for their fixed dates, thus they celebrate the Nativity on 25 December Julian (7 January Gregorian until 2100).

External links

- [http://aa.usno.navy.mil/data/docs/JulianDate.html Julian-Gregorian Converter]
- [http://webexhibits.org/calendars/index.html Calendars through the ages] on WebExhibits.
- [http://www.tyndale.cam.ac.uk/Egypt/ptolemies/chron/roman/chron_rom_cal.htm Roman Dates]
- [http://penelope.uchicago.edu/~grout/encyclopaedia_romana/calendar/romancalendar.html The Roman Calendar]
- [http://5ko.free.fr/jul-greg.php?e=en Synoptical Julian-Gregorian Calendar] - compare the Julian and Gregorian calendars for any date between 1582 and 2100 using this side-by-side reference. Category:Ancient Rome Category:Specific calendars als:Julianischer Kalender ko:율리우스력 ja:ユリウス暦 simple:Julian calendar th:ปฏิทินจูเลียน

Sun

:: For the astrological significance of the Sun, see Solar system in astrology. ::"Solar" redirects here; for the superhero by that name, see Solar (comics). The Sun (or Sol) is the star at the center of our Solar system. Earth orbits the Sun, as do many other bodies, including other planets, asteroids, meteoroids, comets and dust. Its heat and light support almost all life on Earth. The Sun is a ball of plasma with a mass of about 2 kg, which is somewhat higher than that of an average star. About 74% of its mass is hydrogen, with 25% helium and the rest made up of trace quantities of heavier elements. It is thought that the Sun is about 5 billion years old, and is about halfway through its main sequence evolution, during which nuclear fusion reactions in its core fuse hydrogen into helium. In about 5 billion years time the Sun will become a white dwarf. Although it is the nearest star to Earth and has been intensively studied by scientists, many questions about the Sun remain unanswered, such as why its outer atmosphere has a temperature of over 10⁶ K when its visible surface (the photosphere) has a temperature of just 6,000 K. Looking directly at the Sun can damage the retina and one's eyesight. See below for details.

General information

See below The Sun is classified as a main sequence star, which means it is in a state of "hydrostatic balance", neither contracting nor expanding, and is generating its energy through nuclear fusion of hydrogen nuclei into helium. The Sun has a spectral class of G2V, with the G2 meaning that its color is yellow and its spectrum contains spectral lines of ionized and neutral metals as well as very weak hydrogen lines [http://www.astro.uiuc.edu/~kaler/sow/spectra.html#classes], and the V signifying that it, like most stars, is a "dwarf" star on the main sequence[http://www.physics.uq.edu.au/people/ross/phys2080/spec/analyz.htm]. The Sun has a predicted main sequence lifetime of about 10 billion years. Its current age is thought to be about 4.5 billion years, a figure which is determined using computer models of stellar evolution, and