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July 23

July 23

July 23 is the 204th day (205th in leap years) of the year in the Gregorian Calendar, with 161 days remaining.

Events

- 1503 - Orbital calculations suggest that on this day Pluto moved outside Neptune's orbit, remaining there for 233 years.
- 1632 - 300 colonists bound for New France depart Dieppe, France.
- 1829 - In the United States, William Austin Burt patents the first typewriter.
- 1862 - American Civil War: Henry W. Halleck takes command of the Union Army.
- 1903 - Dr. Ernst Pfenning of Chicago, Illinois becomes the first owner of a Ford Model A.
- 1914 - Austria-Hungary issues an ultimatum to Serbia allowing the Austrians to find out who killed Archduke Franz Ferdinand. When Serbia denies Austria-Hungary their demands World War I is sparked on July 28, 1914
- 1926 - Fox Film buys the patents of the Movietone sound system for recording sound onto film.
- 1936 - In Catalonia, Spain, the Unified Socialist Party of Catalonia is founded through the merger of socialist and communist parties.
- 1940 - US Under Secretary of State Sumner Welles`s declaration on the US non-recognition policy of the Soviet annexation and incorporation of three Baltic States - Estonia, Latvia and Lithuania.
- 1942- The Treblinka extermination camp is opened
- 1952 - General Muhammad Naguib leads the Free Officers Movement (formed by Gamal Abdel Nasser - the real power behind the coup) in the overthrow of King Farouk of Egypt.
- 1956 - The Loi Cadre is passed by the French Republic in order to order French overseas territory affairs.
- 1961 - Sandinista National Liberation Front (FSLN) founded in Nicaragua.
- 1962 - Telstar relays the first live trans-Atlantic television signal.
- 1967 - 12th Street Riot: In Detroit, Michigan, one of the worst riots in United States history begins on 12th Street in the predominantly African American inner city (43 killed, 342 injured and ~1,400 buildings burned).
- 1970 - Qaboos ibn Sa’id, becomes Sultan of Oman.
- 1972 - The United States launches Landsat 1, first Earth-resources satellite.
- 1973 - Robert Anton Wilson, the occultist/philosopher, either achieved contact with extraterrestrials from Sirius or started a long-term period of having wild hallucinations, depending on which way you want to look at it.
- 1982 - The International Whaling Commission decides to end commercial whaling by 1985-86.
- 1983 - Gimli Glider: Air Canada flight 143 crash-lands in Gimli, Manitoba.
- 1984 - Vanessa Williams becomes the first Miss America to resign when she surrenders her crown after nude photos of her appeared in Penthouse magazine.
- 1986 - In London, Prince Andrew, Duke of York marries Sarah Ferguson at Westminster Abbey.
- 1997 - Digital Equipment Company files antitrust charges against chipmaker Intel.
- 1999 - Crown Prince Mohammed Ben Al-Hassan, is crowned King Mohammed VI of Morroco at the death of his father.
- 1999 - Hijack of ANA Flight 61 in Tokyo.
- 2001 - Megawati Soekarnoputri becomes the fifth President of Indonesia, replacing Abdurrahman Wahid.
- 2003 - Operation Warrior Sweep is the first major military deployment of the Afghan National Army.
- 2004 - Eleven years after its destruction, Stari most (the Old Bridge) in Mostar is reopened.

Births

- 1301 - Duke Otto of Austria (d. 1339)
- 1339 - King Louis I of Naples (d. 1384)
- 1626 - Sabbatai Zevi, Ottoman Jewish religious leader
- 1649 - Pope Clement XI (d. 1721)
- 1705 - Francis Blomefield, English topographer (d. 1752)
- 1734 - Antonio Maria Gaspare Sacchini, Italian composer (d. 1786)
- 1777 - Philipp Otto Runge, German painter (d. 1810)
- 1796 - Franz Berwald, Swedish composer (d. 1868)
- 1838 - Edouard Judas Colonne, French violinist (d. 1910)
- 1865 - Max Heindel, Danish Christian occultist, astrologer, and mystic (d. 1919)
- 1884 - Emil Jannings, Swiss actor (d. 1950)
- 1886 - Salvador de Madariaga, Spanish League of Nations official (d. 1978)
- 1888 - Raymond Chandler, American author (d. 1959)
- 1892 - Haile Selassie, Emperor of Ethiopia (d. 1975)
- 1893 - Karl Menninger, American psychiatrist (d. 1990)
- 1894 - Arthur Treacher, English character actor (d. 1975)
- 1895 - Aileen Pringle, American actress (d. 1989)
- 1899 - Gustav Heinemann, President of Germany (d. 1976)
- 1906 - Vladimir Prelog, Croatian chemist, Nobel Prize laureate (d. 1998)
- 1918 - Bueno de Mesquita Dutch comedian and actor (d. 2005)
- 1918 - Pee Wee Reese baseball player (d. 1999)
- 1921 - Calvert DeForest, American actor
- 1923 - Witto Aloma, baseball player (d. 1997)
- 1933 - Bert Convy, American game show host, actor, and singer (d. 1991)
- 1936 - Shiv Kumar Batalvi, Punjabi revolutionary (d. 1973)
- 1936 - Don Drysdale, baseball player (d. 1993)
- 1936 - Anthony Kennedy, U.S. Supreme Court Justice
- 1938 - Juliet Anderson, American porn star
- 1938 - Götz George, German actor
- 1938 - Bert Newton, Australian actor and television show host
- 1940 - Don Imus, American talk radio host
- 1942 - Myra Hindley, English murderer (d. 2002)
- 1943 - Tony Joe White, American singer and songwriter
- 1947 - Gardner Dozois, American author
- 1947 - David Essex, English singer
- 1950 - Alex Kozinski, Romanian-born judge
- 1951 - Edie McClurg, American actress
- 1957 - Theo van Gogh, Dutch film director (assassinated) (d. 2004)
- 1961 - Martin Gore, English musician and songwriter (Depeche Mode)
- 1961 - Woody Harrelson, American actor
- 1965 - Slash, English-born guitarist (Guns N Roses)
- 1967 - Philip Seymour Hoffman, American actor
- 1968 - Gary Payton, American basketball player
- 1970 - Thea Dorn, German writer
- 1971 - Dalvin DeGrate, American singer
- 1971 - Alison Krauss, American singer and fiddler
- 1973 - Nomar Garciaparra, baseball player
- 1973 - Francis Healy, Scottish rock musician (Travis)
- 1973 - Monica Lewinsky, White House intern
- 1974 - Terry Glenn, American football player
- 1974 - Maurice Greene, American athlete
- 1974 - Stephanie March, American actress
- 1976 - Judit Polgár, Hungarian chess player
- 1978 - Stefanie Sun, Singapore singer
- 1980 - Michelle Williams, American singer
- 1981 - Steve Jocz, Canadian drummer (Sum41)
- 1983 - Rebecca Cartwright, Australian actress
- 1986 - Tomas Cunha e Silva, Portuguese driver
- 1989 - Daniel Radcliffe, English actor

Deaths

- 1227 - Qiu Chuji, Chinese Taoist (b. 1148)
- 1373 - Saint Birgitta, Swedish saint (b. 1303)
- 1403 - Thomas Percy, 1st Earl of Worcester, English rebel (executed) (born 1343)
- 1531 - Louis de Brézé, seigneur d'Anet, Marshal of Normandy and husband of Diane de Poitiers
- 1584 - John Day, English printer (b. 1522)
- 1692 - Gilles Ménage, French scholar (b. 1613)
- 1727 - Simon Harcourt, 1st Viscount Harcourt, Lord Chancellor of Great Britain
- 1757 - Domenico Scarlatti, Italian composer (b. 1685)
- 1764 - Gilbert Tennent, Irish-born religious leader (b. 1703)
- 1773 - George Edwards, English naturalist (b. 1693)
- 1781 - John Joachim Zubly, Swiss-born Continental Congressman (b. 1724)
- 1793 - Roger Sherman, American signer of the Declaration of Independence (b. 1721)
- 1853 - Andries Pretorius, Boer leader (b. 1798)
- 1878 - Carl Freiherr von Rokitansky, Bohemian physician (b. 1804)
- 1885 - Ulysses S. Grant, 18th President of the United States (b. 1822)
- 1916 - Sir William Ramsay, Scottish chemist, Nobel Prize laureate (b. 1852)
- 1920 - Conrad Kohrs, German-born rancher (b. 1835)
- 1924 - Frank Frost Abbott, American classical scholar (b. 1850)
- 1942 - Adam Czerniakow, Polish engineer (suicide) (b. 1880)
- 1948 - D. W. Griffith, American film director (b. 1875)
- 1951 - Henri Philippe Pétain, leader of Vichy France (b. 1856)
- 1955 - Cordell Hull, United States Secretary of State, recipient of the Nobel Peace Prize (b. 1871)
- 1966 - Montgomery Clift, American actor (b. 1920)
- 1968 - Henry Hallett Dale, English scientist, recipient of the Nobel Prize in Physiology or Medicine (b. 1875)
- 1971 - Van Heflin, American actor (b. 1910)
- 1973 - Eddie Rickenbacker, American pilot (b. 1890)
- 1982 - Vic Morrow, American actor (b. 1929)
- 1983 - Georges Auric, French composer (b. 1899)
- 1985 - Johnny Wardle, English cricketer (b. 1923)
- 1989 - Donald Barthelme, American author (b. 1931)
- 1997 - Chuhei Nambu, Japanese athlete (b. 1904)
- 1999 - King Hassan II of Morocco (b. 1929)
- 2001 - Eudora Welty, American author (b. 1909)
- 2002 - Leo McKern, Australian actor (b. 1920)
- 2002 - Dr. William L. Pierce, American author and activist (b. 1933)
- 2002 - Chaim Potok, American novelist and rabbi (b. 1929)
- 2003 - James E. Davis, New York City councilman (murdered) (b. 1962)
- 2004 - Mehmood, Indian actor (b. 1932)
- 2004 - Carlos Paredes, Portuguese musician and composer (b. 1925)

Holidays and observances

- Egypt - Revolution Day (1952)
- Libya - Revolution Day
- Papua New Guinea - Remembrance Day
- Roman Empire - Neptunalia held in honor of Neptune
- Rastafari movement - Celebration of the birthday of Haile Selassie
- Astrology: First day of sun sign Leo

External links

- [http://news.bbc.co.uk/onthisday/hi/dates/stories/july/23 BBC: On This Day]
- [http://www.tnl.net/when/7/23 This Day in History] ---- July 22 - July 24 - June 23 - August 23 -- listing of all days ko:7월 23일 ms:23 Julai ja:7月23日 simple:July 23 th:23 กรกฎาคม

July 23

July 23 is the 204th day (205th in leap years) of the year in the Gregorian Calendar, with 161 days remaining.

Events

Births

Deaths

Holidays and observances

External links

Leap year

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. Seasons and astronomical events do not repeat at an exact number of days, so a calendar which had the same number of days in each year would over time drift with respect to the event it was supposed to track. By occasionally inserting (or intercalating) an additional day or month into the year, the drift can be corrected. Leap years (which keep the calendar in sync with the year) should not be confused with leap seconds (which keep clock time in sync with the day).

Gregorian calendar

The Gregorian calendar, the current standard calendar in most of the world, adds a 29th day to February in all years evenly divisible by 4, except for century years (those ending in -00), which receive the extra day only if they are evenly divisible by 400. Thus 1996 was a leap year whereas 1999 was not, and 1600, 2000 and 2400 are leap years but 1700, 1800, 1900 and 2100 are not. The reasoning behind this rule is as follows:
- The Gregorian calendar is designed to keep the vernal equinox on or close to March 21, so that the date of Easter (celebrated on the Sunday after the 14th day of the Moon that falls on or after 21 March) remains correct with respect to the vernal equinox.
- The vernal equinox year is currently about 365.242375 days long.
- The Gregorian leap year rule gives an average year length of 365.2425 days. This difference of a little over 0.0001 days means that in around 8,000 years, the calendar will be about one day behind where it should be. But in 8,000 years' time the length of the vernal equinox year will have changed by an amount we can't accurately predict (see below). So the Gregorian leap year rule does a good enough job. Image:Gregoriancalendarleap.png

Which day is the leap day?

The Gregorian calendar is a modification of the Julian calendar first used by the Romans. The Roman calendar originated as a lunar calendar (though from the 5th century BC it no longer followed the real moon) and named its days after three of the phases of the moon: the new moon (calends, hence "calendar"), the first quarter (nones) and the full moon (ides). Days were counted down (inclusively) to the next named day, so 24 February was ante diem sextum calendas martii ("the sixth day before the calends of March"). Since 45 BC, February in a leap year had two days called "the sixth day before the calends of March". The extra day was originally the second of these, but since the third century it was the first. Hence the term bissextile day for 24 February in a bissextile year. Where this custom is followed, anniversaries after the inserted day are moved in leap years. For example, the former feast day of Saint Matthias, 24 February in ordinary years, would be 25 February in leap years. This historical nicety is, however, in the process of being discarded: The European Union declared that, starting in 2000, 29 February rather than 24 February would be leap day, and the Roman Catholic Church also now uses 29 February as leap day. The only tangible difference is felt in countries that celebrate feast days.

Julian calendar

The Julian calendar adds an extra day to February in years divisible by 4. This rule gives an average year length of 365.25 days. The excess of about 0.0076 days with respect to the vernal equinox year means that the vernal equinox moves a day earlier in the calendar every 130 years or so.

Revised Julian Calendar

The Revised Julian calendar adds an extra day to February in years divisible by 4, except for years divisible by 100 that do not leave a remainder of 200 or 600 when divided by 900. This rule agrees with the rule for the Gregorian calendar until 2799. The first year that dates in the Revised Julian calendar will not agree with the those in the Gregorian calendar will be 2800, because it will be a leap year in the Gregorian calendar but not in the Revised Julian calendar. This rule gives an average year length of 365.242222… days. This is a very good approximation to the mean tropical year, but because the vernal equinox tropical year is slightly longer, the Revised Julian calendar does not do as good a job as the Gregorian calendar of keeping the vernal equinox on or close to 21 March.

Chinese calendar

The Chinese calendar is lunisolar, so a leap year has an extra month, often called an embolismic month after the Greek word for it. In the Chinese calendar the leap month is added according to a complicated rule, which ensures that month 11 is always the month that contains the northern winter solstice. The intercalary month takes the same number as the preceding month; for example, if it follows the second month then it is simply called "leap second month".

Hebrew calendar

The Hebrew calendar is also lunisolar with an embolistic month. In the Hebrew calendar the extra month is called Adar Alef (first Adar) and is added before Adar, which then becomes Adar Sheni (second Adar). According to the Metonic cycle, this is done seven times every nineteen years, specifically, in years, 3, 6, 8, 11, 14, 17, and 19. In addition, the Hebrew calendar has postponement rules that postpone the start of the year by one or two days. The year before the postponement gets one or two extra days, and the year whose start is postponed loses one or two days. These postponement rules reduce the number of different combinations of year length and starting day of the week from 28 to 14, and regulate the location of certain religious holidays in relation to the Sabbath.

Hindu Calendar

In the Hindu calendar, which is a lunisolar calendar, the embolismic month is called adhika maas (extra month). It is the month in which the sun is in the same sign of the stellar zodiac on two consecutive dark moons.

Iranian calendar

The Iranian calendar also has a single intercalated day once in every four years, but every 33 years or so the leap years will be five years apart instead of four years apart. The system used is more accurate and more complicated, and is based on the time of the March equinox as observed from Teheran. The 33-year period is not completely regular; every so often the 33-year cycle will be broken by a cycle of 29 or 37 years.

Long term leap year rules

The accumulated difference between the Gregorian calendar and the vernal equinoctial year amounts to 1 day in about 8,000 years. This suggests that the calendar needs to be improved by another refinement to the leap year rule: perhaps by avoiding leap years in years divisible by 8,000. (The most common such proposal is to avoid leap years in years divisible by 4,000 [http://www.google.com/search?q=%22gregorian+calendar%22+error+%22leap+year%22+4000]. This is based on the difference between the Gregorian calendar and the mean tropical year. Others claim, erroneously, that the Gregorian calendar itself already contains a refinement of this kind [http://www.straightdope.com/mailbag/mleapyr.html].) However, there is little point in planning a calendar so far ahead because over a timescale of tens of thousands of years the number of days in a year will change for a number of reasons, most notably: #Precession of the equinoxes moves the position of the vernal equinox with respect to perihelion and so changes the length of the vernal equinoctial year. #Tidal acceleration from the sun and moon slows the rotation of the earth, making the day longer. In particular, the second component of change depends on such things as post-glacial rebound and sea level rise due to climate change. We can't predict these changes accurately enough to be able to make a calendar that will be accurate to a day in tens of thousands of years.

Marriage proposal

There is a tradition, said to go back to Saint Patrick and Saint Bridget in 5th century Ireland, whereby women may only make marriage proposals in leap years.

Saint Patrick and the leap year

:Saint Patrick, having driven the frogs out of the bogs was walking along the shores of Lough Neagh, when he was accosted by Saint Bridget in tears, and was told that a mutiny had broken out in the nunnery over which she presided, the ladies claiming the right of popping the question. :Saint Patrick said he would concede them the right every seventh year, when Saint Bridget threw her arms round his neck, and exclaimed, "Arrah, Pathrick, jewel, I daurn't go back to the girls wid such a proposal. Make it one year in four." Saint Patrick replied, "Bridget, acushla, squeeze me that way again, an' I'll give ye leap-year, the longest of the lot." Saint Bridget, upon this, popped the question to St Patrick himself, who, of course, could not marry: so he patched up the difficulty as best he could with a kiss and a silk gown. (Source: Evans, Ivor H, Brewer's Dictionary of Phrase and Fable, Cassell, London, 1988) According to a 1288 law in Scotland, fines were levied if the proposal was refused by the man; compensation ranged from a kiss to a silk gown to soften the blow. Because men felt that put them at too great a risk, the tradition was in some places tightened to restricting female proposals to 29 February.

Birthdays

A person who was born on 29 February may be called a "leapling". In non-leap years they usually celebrate their birthday on 28 February or 1 March. There are many instances in children's literature where a person's claim to be only a quarter of their actual age turns out be based on counting their leap-year birthdays. A similar device is used in the plot of the Gilbert and Sullivan operetta The Pirates of Penzance. Category:Calendars Category:Units of time als:Schaltjahr ko:윤년 ja:閏年 simple:Leap year th:ปีอธิกสุรทิน

1503

Events

- January 20 - Seville in Castile is awarded exclusive right to trade with the New World.
- April 21 - Battle of Cerignola. Aragonese forces under Gonzalo Fernández de Córdoba defeat the French under the Duc de Nemours, who is killed. Considered to be the first battle in history won by gunpowder small arms.
- May 10 - Christopher Columbus discovers the Cayman Islands and he names them Las Tortugas after the numerous sea turtles there.
- May 13 - Capture of Naples by the Spanish.
- July 23 - Orbital calculations suggest that on this day Pluto moved outside Neptune's orbit, remaining there for 233 years.
- August 8 - King James IV of Scotland marries Margaret Tudor, daughter of King Henry VII of England at Holyrood Abbey, Edinburgh, Scotland.
- September 22 - Francesco Todeschini Piccolomini becomes Pope Pius III succeeding Pope Alexander VI, but dies on October 18.
- December 29 - Battle of the Garigliano - Spanish forces under Cordoba defeat a French-Italian mercenary army under the Marquis of Saluzzo. The French forces withdraw to Gaeta.
- Giuliano della Rovere becomes Pope Julius II succeeding Pope Pius III.
- Leonardo da Vinci starts work on the Mona Lisa.
- Perpendicular style chapel added to Westminster Abbey.
- Battle of Ruvo - French-Spanish Wars in Italy.
- Vasco da Gama established India's first Portuguese fortress at Cochin.
- Mariotto Albertinelli paints his masterpiece, the "Visitation of the Virgin".

Births

- January 11 - Girolamo Francesco Maria Mazzola, Italian artist (d. 1540)
- March 10 - Ferdinand I, Holy Roman Emperor (died 1564)
- March 22 - Antonio Francesco Grazzini, Italian writer (died 1583)
- June 1 - Wilhelm von Grumbach, German adventurer (died 1567)
- June 28 - Giovanni della Casa, Italian poet (died 1556)
- June 30 - John Frederick, Elector of Saxony (died 1554)
- August 12 - Christian III of Denmark and Norway (died 1559)
- November 17 - Agnolo di Cosimo, Italian artist and poet (d. 1572)
- December 14 - Nostradamus, French physician and prophet (died 1566)
- Nicholas Bourbon, French poet
- Lucas David, Prussian historian (died 1583)
- Robert Estienne, French printer (died 1559)
- Charles Etienne, French anatomist (died 1564)
- John Frith, English protestant priest and martyr (died 1533)
- Henry II of Navarre (died 1555)
- Shimazu Katsuhisa, Japanese nobleman
- Parmigianino, Italian painter (died 1540)
- Garcilaso de la Vega, Spanish poet (died 1536)

Deaths

- February 11 - Elizabeth of York, queen of Henry VII of England (born 1466)
- May 20 - Lorenzo di Pierfrancesco de' Medici, Italian patron of the arts (b. 1463)
- June 30 - Pierre d'Aubusson, Grand Master of the Knights of Rhodes (born 1423)
- August 18 - Pope Alexander VI (born 1431)
- October 18 - Pope Pius III (born 1439)
- November 23 - Margaret of York, wife of Charles I, Duke of Burgundy (b. 1446)
- December 28 - Piero di Lorenzo de' Medici, ruler of Florence (born 1471)
- Richard Amerike, English merchant and patron of John Cabot (born 1445)
- Peter II, Duke of Bourbon (born 1438)
- Reginald Bray, British courtier (born 1440)
- Edward Story, Bishop of Carlisle and Chichester Category:1503 ko:1503년 simple:1503

Pluto

: For more uses of the term Pluto, see Pluto (disambiguation). Pluto is the ninth planet in the solar system. Discovered in 1930 and immediately classified as a planet, its status is currently under dispute. Pluto has an eccentric orbit that is highly inclined in respect to the other planets and takes it inside the orbit of Neptune. Its largest moon is Charon, discovered in 1978; two smaller moons were discovered in 2005. Pluto's astronomical symbol is a P-L monogram, . This represents both the first two letters of the name Pluto and the initials of Percival Lowell, the man who lent his name to the observatory that was used to find Pluto. An alternate symbol resembles that of Neptune, but has a circle in place of the middle spoke in the top center. Due to its size and unusual orbit, there has been debate regarding Pluto's classification as a major or a minor planet, and there is increasing momentum for recognizing "dual status." Pluto is classified as a trans-Neptunian object. As of July 31, 2005, one other trans-Neptunian object, , had been found that is larger than Pluto.

Discovery and naming

Pluto was discovered by the astronomer Clyde Tombaugh at the Lowell Observatory in Arizona on February 18, 1930 after an extensive search when he compared photographic plates taken on January 23 and 29. After the observatory obtained confirming photographs, the news of the discovery was telegraphed to the Harvard College Observatory on March 13, 1930. The planet was later found on photographs dating back to March 19, 1915. Tombaugh was searching for a "Planet X" to explain discrepancies in the predicted orbit of Neptune. It is now known these discrepancies were an artifact of the slightly incorrect value then assumed for the mass of Neptune. In the matter of Pluto the discretion of naming the new object belonged to Lowell Observatory and its director, Vesto Melvin Slipher, who, in the words of Tombaugh, was "urged to suggest a name for the new planet before someone else did". Soon suggestions began to pour in from all over the world. Constance Lowell, Percival's widow who had delayed the search through her lawsuit, proposed Zeus, then Lowell, and finally her own first name, none of which met with any enthusiasm. One young couple even wrote to ask that the planet be named after their newborn child. Mythological names were much to the fore: Cronus and Minerva (proposed by the New York Times, unaware that it had been proposed for Uranus some 150 years earlier) were high on the list. Also there were Artemis, Athene, Atlas, Cosmos, Hera, Hercules, Icarus, Idana, Odin, Pax, Persephone, Perseus, Prometheus, Tantalus, Vulcan, Zymal, and many more. One complication was that many of the mythological names had already been allotted to the numerous asteroids. Virtually all the female names had been used up, and male names were usually reserved for objects with unusual orbits. The name retained for the planet is that of the Roman god Pluto, and it is also intended to evoke the initials of the astronomer Percival Lowell, who predicted that a planet would be found beyond Neptune. The name was first suggested by Venetia Burney, at the time an eleven-year-old girl from Oxford, England. Over the breakfast table, one morning her grandfather, who worked at Oxford University's Bodleian Library, was reading about the discovery of the new planet in the Times newspaper. He asked his granddaughter what she thought would be good name for it. Venetia thought that as it was so cold and so distant it should be named after the Roman God of the underworld. Professor Herbert Hall Turner cabled his colleagues in America with this suggestion, and after favourable consideration which was almost unanimous, the name Pluto was officially adopted and an announcement made by Slipher on May 1, 1930. The Chinese, Korean, Japanese, and Vietnamese now call the planet 冥王星. Because Pluto was nowhere near the asteroid belt (trans-Neptunian objects would not be discovered until much later), it never got an asteroidal provisional designation; had it obtained one, it would probably have been "1930 BD".

Orbit

provisional designation Pluto's orbit is unlike those of the other planets. It is highly inclined above the plane of the ecliptic, and highly eccentric (non-circular). The eccentricity of its orbit is such that it crosses the orbit of Neptune, and making Pluto only the eighth-most distant planet from the Sun for part of each orbit; the most recent occurrence of this phenomenon lasted from February 7, 1979 through February 11, 1999. Mathematical calculations indicate that the previous occurrence only lasted fourteen years from July 11, 1735 to September 15, 1749. However, the same calculations indicate that Pluto was the eighth-most distant planet between April 30, 1483 and July 23, 1503, which is almost exactly the same length as the 1979 to 1999 period. Recent studies suggest each crossing of Pluto to inside Neptune's orbit lasts alternately for approximately thirteen and twenty years with minor variations. 1503 compared to the other planets]]Pluto orbits in a 3:2 orbital resonance with Neptune. When Neptune approaches Pluto from behind their gravity start to pull on each other slightly, resulting in an interaction between their positions in orbit of the same sort that produces Trojan points. Since the orbits are eccentric, the 3:2 periodic ratio is favoured because this means Neptune always passes Pluto when they're almost farthest apart. Half a Pluto orbit later, when Pluto is nearing its closest approach, it initially seems as if Neptune is about to catch up to Pluto. But Pluto speeds up due to the gravitational acceleration from the Sun, stays ahead of Neptune, and pulls ahead until they meet again on the other side of Pluto's orbit. Beginning in the 1990s, other trans-Neptunian objects have been discovered, and a certain number of these also have a 3:2 orbital resonance with Neptune. TNOs with this orbital resonance are named "plutinos", after Pluto.

Physical characteristics

More than 75 years after its discovery, many facts about Pluto remain unknown, mainly due to the fact that it is the only planet that has not been visited by human spacecraft and that it is too far away for in-depth investigations with telescopes from earth. What is known are the few physical properties listed below.

Mass and size

Pluto is not only smaller and much less massive than every other planet, at less than 0.2 lunar masses it is also smaller and less massive than seven moons: Ganymede, Titan, Callisto, Io, Earth's Moon, Europa and Triton. However, Pluto is more than twice the diameter, and a dozen times the mass, of Ceres, the largest minor planet in the asteroid belt, and it was larger than any other object known in the trans-Neptunian Kuiper belt until was announced in 2005. See List of solar system objects by mass and List of solar system objects by radius. Pluto's mass and diameter could only be estimated for many decades after its discovery. The discovery of its satellite Charon in 1978 enabled a determination of the mass of the Pluto-Charon system by simple application of Newton's formulation of Kepler's third law. Later Pluto's diameter was measured when it was occulted by Charon, and its disk can now be resolved by telescopes using adaptive optics.

Atmosphere

Pluto's thin atmosphere is most likely nitrogen and carbon monoxide, in equilibrium with solid nitrogen and carbon monoxide ices on the surface. As Pluto moves away from its perihelion and farther from the Sun, more of its atmosphere freezes. Pluto was found to have an atmosphere from an occultation observation in 1988. When an object with no atmosphere occults a star, the star abruptly disappears; in the case of Pluto, the star dimmed out gradually. From the rate of dimming, the atmosphere was determined to have a pressure of 0.15 Pa, roughly 1/700,000 that of earth. In 2002, another occultation of a star by Pluto was observed and analyzed by teams led by Bruno Sicardy of the Paris Observatory [http://calys.obspm.fr/~sicardy/pluton/pr_obs_en.html] and by Jim Elliot of MIT [http://web.mit.edu/newsoffice/2002/pluto.html] and Jay Pasachoff of Williams College [http://www.williams.edu/admin/news/releases.php?id=162]. Surprisingly, the atmosphere was estimated to have a pressure of 0.3 Pa, even though Pluto was further from the Sun than in 1988, and hence should be colder and have a less dense atmosphere. The current best hypothesis is that the south pole of Pluto came out of shadow for the first time in 120 years in 1987, and extra nitrogen sublimated from a polar cap. It will take decades for the excess nitrogen to condense out of the atmosphere.

Appearance

Pluto's apparent magnitude is fainter than 14 m and therefore a telescope is required for observation. To be easily seen, a telescope of around 30 cm aperture is desirable. It looks star-like even in very big telescopes, because its angular diameter is only 0.15″. The colour of Pluto is light brown with a very slight tint of yellow.

Pluto's moons

apparent magnitude Pluto has three known natural satellites: Charon, first identified in 1978, and two smaller, as yet unnamed moons discovered in 2005.

Charon

The Pluto-Charon system is noteworthy for being the only planet/moon system in the solar system whose barycenter lies above the planet's surface, thus prompting some astronomers to label it a double planet (a term complicated by the discovery of two more Plutonian moons). The Pluto-Charon system is also unusual among planetary systems in that they are tidally locked to each other: Charon always presents the same face to Pluto, and Pluto also always presents the same face to Charon. The discovery of Charon allowed astronomers to determine the mass of the Pluto-Charon pair from their observed orbital period and separation by a straightforward application of Kepler's third law of planetary motion. The mass was found to be lower than even the lowest earlier estimates. The discovery also led astronomers to alter their estimate of Pluto's size. Originally, it was believed that Pluto was larger than Mercury but smaller than Mars, but that calculation was based on the premise that a single object was being observed. Once it was realized that there were in fact two objects instead of one, the estimated size of Pluto was revised downward. Today, with modern adaptive optics, Pluto's disc can be resolved and thus its size can be directly determined. adaptive optics Charon's discovery also resulted in the calculation of Pluto's albedo being revised upward; since the planet was now seen as being far smaller than originally estimated, by necessity its capacity to reflect light must be greater than what had been formerly believed. Current estimates place Pluto's albedo as marginally less than that of Venus, which is fairly high. Previously, some researchers had theorized that Pluto and its moon Charon were moons of Neptune that were knocked out of Neptunian orbit when Triton was captured. Triton, the largest moon of Neptune, which shares many atmospherical and geological composition similarities with Pluto, may once have been a Kuiper belt object in a solar orbit, and today it is widely accepted that Pluto never orbited Neptune. An occultation of a star by Charon in 2005, observed in South America by teams from MIT-Williams College, the Paris Observatory, and the Southwest Research Institute has led to improved knowledge of Charon's parameters.

The outer moons

Charon (right) & S/2005 P 1 (bright dot on left)]] Two additional moons were imaged by astronomers working with the Hubble Space Telescope on May 15, 2005, and have received provisional designations of S/2005 P 1 and S/2005 P 2. They were confirmed with "precovery" Hubble images from June 14, 2002. Observations suggest they orbit Pluto at at least twice the distance Charon does. P2 stays about 49,000km from the planet, P1 lies even further away at 65,000km. The two candidate moons seem to orbit Pluto in an anti-clockwise direction. Preliminary observations are also consistent with the outer moons lying in the same orbital plane as Charon, and orbiting at distances two and three times farther away, with orbital resonances of 4:1 and 6:1 with Charon. Both objects appear to be on the order of 50-150 km in diameter, compared to Charon's 1,200 km, and are thought to have masses less than 0.3% of Charon's (or 0.03% of Pluto's mass). The discovery team plans follow-up observations with Hubble in February 2006 to work out the precise orbits, but ground-based observatories will attempt to image the moons as well. Once the orbits are confirmed, the moons can be given permanent names. [http://www.nasa.gov/vision/universe/solarsystem/hubble_pluto.html] [http://news.bbc.co.uk/2/hi/science/nature/4396546.stm]

Exploration of Pluto

Little is known about Pluto because of its great distance from Earth and because no exploratory spacecraft have visited Pluto yet. The Voyager 1 probe was originally intended to visit Pluto, but due to budget cuts and lack of interest — before the discovery of Pluto's moon, size, and atmosphere — the flyby was scrapped in order to facilitate a close flyby of Saturn's moon Titan. The first spacecraft to visit Pluto will be NASA's New Horizons, a mission led by the Southwest Research Institute and the Johns Hopkins Applied Physics Laboratory. The mission's launch window is between January 11 and February 14, 2006. Assuming it launches within the first 23 days of the window, it will benefit from a gravity assist from Jupiter, and arrive at Pluto in July 2015. New Horizons weighs half a ton and will travel at speeds reaching 43,000 km/h (27,000 mph). It will use a remote sensing package that includes imaging instruments and a radio science investigation, as well as spectroscopic and other experiments, to characterize the global geology and morphology of Pluto and its moon Charon, map their surface composition and characterize Pluto's neutral atmosphere and its escape rate. The mission plan also calls for a flyby of one or more Kuiper belt objects by 2022. The New Horizons mission replaced the Pluto Kuiper Express mission, which was cancelled in 2000 because of increasing costs and launch vehicle delays.

The Pluto debate

Planet X?

The planet Pluto was originally discovered in 1930 in the course of a search for a body sufficiently massive to account for supposed anomalies in the orbits of Uranus and Neptune. Once it was found, its faintness and failure to show a visible disc cast doubt on the idea that it could be Lowell's Planet X. Lowell had made a prediction of Pluto's position in 1915 which had turned out to be fairly close to its actual position at that time; however Ernest W. Brown concluded almost immediately that this was a coincidence, and this view is retained today. Lowell had also made earlier, different predictions of Planet X's position beginning in 1902. [http://www.phys-astro.sonoma.edu/people/faculty/tenn/asphistory/1994.html] In the following decades estimates of the Plutonian mass and diameter were the subject of debate as telescopes and imaging systems improved. The consensus steadily favored smaller masses and diameters as time passed. Indeed, one observer waggishly pointed out that if the trend were extrapolated, the planet seemed to be in danger of vanishing altogether, a remark which proved possibly prophetic in light of later debates over Pluto's status as a "planet". In an attempt to reconcile Pluto's small apparent size with its identification as Planet X, the theory of specular reflection was proposed. This held that observers were measuring only the diameter of a bright spot on the highly reflective surface of a much larger planet which could thereby be massive without having an exceptionally high density. The uncertainty was conclusively resolved by the discovery of Pluto's satellite Charon in 1978. This made it possible to determine the combined mass of the Pluto-Charon system which turned out to be lower even than that anticipated by skeptics of the specular reflection theory, which was then rendered completely untenable. The accepted figure for Pluto's diameter today makes it considerably smaller than the Moon, with only a fraction of the Moon's mass on account of its being largely composed of ice. More recently, measurements of the path of Voyager 2 have shown that Neptune has a lower mass than previously believed and that when this lower mass is taken into account there is no anomalous movement of Uranus or Neptune. Thus Pluto's discovery and Lowell's 1915 prediction were largely coincidental as Pluto actually has no role in what were believed to be anomalies in Neptune and Uranus' motion. Pluto's discovery was mostly due to the thoroughness and diligence of Tombaugh's search, which he continued for some time after the discovery and left him satisfied that no other planet of a comparable magnitude existed. While Pluto's identification as Planet X began to be doubted soon after its discovery, and for some decades afterwards some considered that a hypothetical tenth planet might be the true Planet X which supposedly caused anomalies in Uranus and Neptune's position, Pluto's identity as the solar system's ninth planet was unquestioned until the 1990s.

Minor planet?

1990s Starting in September of 1992 scientists began discovering hundreds of other bodies in the area of the solar system beyond the orbit of Neptune. The second of these, after Pluto and Pluto's moon Charon, was . The continued discovery of these objects, especially of plutinos, rekindled a debate that goes on to this day: is Pluto a major planet or simply one of the largest trans-Neptunian objects? Trans-Neptunian objects are considered to be minor planets, so the question arose whether to consider Pluto to be one too. This planetary sciences debate landed in newspaper headlines, editorials, and on the Internet in the mid- to late-1990s. Thoughts that Pluto might be "demoted" to non-planet status created an emotional response in certain sectors of the public. Such news outlets as the BBC News Online, the Boston Globe, and USA Today all printed stories noting that the International Astronomical Union was considering dropping Pluto's planetary status. "Save Pluto" websites sprang up, and school children sent letters to astronomers and the IAU. On February 3 1999, Brian Marsden of the Minor Planet Center inadvertently fueled the debate when he issued an editorial in the [http://cfa-www.harvard.edu/iau/mpec/J99/J99C03.html Minor Planet Electronic Circular 1999-C03] noting that the 10,000th minor planet was about to be numbered and this called for a large celebration (the IAU celebrates every thousandth numbered minor planet in some way). He suggested that Pluto be honored with the number 10,000, giving it "dual citizenship" of sorts as both a major and a minor planet. Between the media reports and the Minor Planet Electronic Circulars, IAU General Secretary Joannes Anderson issued a press release that same day, stating there were no plans to change Pluto's planetary status. Eventually, the number 10,000 was assigned to an "ordinary" asteroid, 10000 Myriostos. The debate centers on how a "planet", from the Greek for "wanderer", is an appellation that depends upon an object's particular size, formation, or orbit. Some argue that not only is Pluto a major planet but also some moons like Titan, Europa or Triton, or even the larger asteroids. Some argue that an astronomical object more than about 360 km in diameter, at which point the object has a tendency to become round under its own gravity, should be known as a major planet; this would include several moons and a handful of asteroids. Isaac Asimov suggested the term mesoplanet be used for planetary objects intermediate in size between Mercury, the smallest terrestrial planet with a diameter of 4879.4 km and Ceres, the largest known asteroid with a mean diameter of 950 km, which would include Pluto but not most moons.

New discoveries

Continuing discoveries in the transneptunian region keep rekindling the debate. In 2002, 50000 Quaoar was discovered, with a 1280 km diameter, making it a bit more than half the size of Pluto. Another recent discovery, 90482 Orcus, is probably even larger. In 2004 the discoverers of 90377 Sedna, an extremely distant object well beyond the other known transneptunian objects, placed an upper limit of 1800 km on its diameter, close to Pluto's 2320 km. On July 29, 2005, a Trans-Neptunian object called was announced, which on the basis of its magnitude and simple albedo considerations is assumed to be larger than Pluto. This caused its discoverers to call it the "10th planet" of the solar system, although there is no consensus yet on whether to call it a planet, and others consider the new discovery to be the strongest argument yet for demoting Pluto to the status of a minor planet. could be the largest object yet discovered in the solar system since Neptune in 1846. The last remaining distinguishing feature of Pluto is now its large moon, Charon, and its atmosphere; these characteristics may not, however, be unique to Pluto: several other transneptunian objects are known to have satellites; and 's spectrum suggests that it has a similar surface composition to Pluto, as well as a moon discovered in September of 2005. There is some historical precedent for "demoting" a "planet" in the light of subsequent discoveries. The first four asteroids (1 Ceres, 2 Pallas, 3 Juno and 4 Vesta) were considered to be planets for several decades (in part because their sizes were not accurately known at the time). However, in 1845, the first new asteroid in 38 years was discovered (5 Astraea), just one year before Neptune, and soon every year brought more asteroid discoveries. It was soon recognized that Ceres and the others were just the most prominent members of a populous asteroid belt, and although asteroids are also known as "minor planets", they are no longer considered "planets". Some see in this a precedent for noting that Pluto is just the most prominent member of the Kuiper belt. On the other hand, it may very well be that regardless of future astronomical discoveries, Pluto will remain grandfathered as a planet in much the same way that Europe is considered a separate continent for historical reasons although geographically it makes more sense, from first principles, to consider both Europe and Asia to comprise the single continent of Eurasia.

Pluto in popular culture

- Donald W. Horner, in Their Winged Destiny (1912), described spaceflight to Alpha Centauri by astronauts who, as they leave the solar system, pass a planet beyond Neptune.
- Mickey Mouse's dog Pluto first appeared in the 1930 cartoon The Chain Gang; it was adapted into Minnie Mouse's dog Rover, and shortly thereafter became Mickey's Pluto, being named for the planet.
- Stanton Coblentz's In Plutonian Depths (Wonder Stories Quarterly, Spring 1931) was the first story to take advantage of the newly discovered and named world.
- In H. P. Lovecraft's Cthulhu mythos stories (1928–), the Mi-go are a fictional alien race with a base on Pluto, called Yuggoth and Iukkoth in the stories. There are some stories, though, that identify Yuggoth with a huge world situated beyond Pluto on an orbit perpendicular to the ecliptic.
- In Robert A. Heinlein's novel Have Space Suit-Will Travel (1958), Pluto is used by aliens as a remote base for Earth exploration. In Heinlein's story Sky Lift (1953), a torch-ship pilot flies on a mercy mission to Pluto.
- In Larry Niven's novel World of Ptavvs (1966), Pluto was theorized to have been a moon of Neptune until it was knocked out of orbit by an interstellar craft.
- Martinex of the Guardians of the Galaxy is the last survivor of a human colony in Pluto. His ancestors were African. The character first appeared in January, 1969 and operates in the 31st century.
- In the 1974 Japanese anime series Space Battleship Yamato, also known as Star Blazers, the eponymous starship destroys an alien base on Pluto and fights a subsequent battle in an asteroid belt beyond Pluto. Eighteen years later astronomers confirmed the existence of the real-life Kuiper belt.
- In the Doctor Who (1963–) serial The Sun Makers (1977), set far in the future, Pluto is covered with vast cities that are warmed by artificial suns, but access to sunlight is controlled by a sinister ruling elite.
- In John DeChancie's Starrigger series (1983), Pluto is the location of our solar system's dimensional gate to the interstellar Skyway.
- Pluto is featured in Kim Stanley Robinson's novel Icehenge (1985), in which a mysterious artificial structure is found on the planet's north pole.
- In the computer game Star Control II (1990), and consequently in The Ur-Quan Masters, the Spathi Captain Fwiffo can be found on Pluto.
- The final section of Dave Sim's graphic novel Minds (Cerebus the Aardvark, Volume 10, 1996) takes place on Pluto.
- Christine Lavin's song Planet X (1996) is a good-natured protest against suggestions that Pluto is not a planet.
- In the Japanese anime series Cowboy Bebop (1998), it is mentioned that a "supermax" maximum security penitentiary is located on Pluto.
- In the game Starsiege (1999), Pluto is destroyed at the end of the game.
- The television show Futurama (1999-2003) has featured Pluto on occasion, mainly as a habitat for penguins.
- In the television show Aqua Teen Hunger Force (2000), two of the show's "Villains", Oglethorpe and Emory (The Plutonians), are from Pluto.
- In the cartoon Fairly Oddparents (2001–) Cosmo destroys Pluto with a button the president lost.
- In the anime Bishoujo Senshi Sailor Moon, Sailor Pluto is the third Outer Senshi to be discovered, and her talisman is the Garnet Orb. She guards the gates of time, and her Greek god equivalent is Hades, the lord of the underworld, which she derives her attacks from (e.g. Dead Scream). On her forehead, she bears the planet's symbol and her image colour is black (sometimes purple).
- In the game Epoch Star (2004), Pluto is the home planet of the Anthropite civilization.
- In the second part of a BBC drama documentary called [http://www.bbc.co.uk/sn/tvradio/programmes/spaceodyssey/ Space Odyssey: Voyage to the Planets] (2004) Pluto is the penultimate destination on a hypothetical human space flight to planets of the Solar System
- In the PC Game Freelancer, one of the start movies shows Pluto Being Destroyed by an alien race 800 years before the game starts.

References

- Henderson, Mark (Oct. 30, 2005). "Pluto may lose status of planet". New Straits Times, p. F17.

External links

- [http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html NASA's Pluto fact sheet]
- [http://www.studyworksonline.com/cda/content/article/0%2C%2CEXP666_NAV4-42_SAR920,00.shtml StudyWorks! Online: Is Pluto a Planet?] - summarizes the pros and the cons of classifying Pluto as a planet
- David H. Freedman, [http://www.theatlantic.com/issues/98feb/pluto.htm "When is a Planet Not a Planet?"], Atlantic Monthly, February 1998.
- [http://pluto.jhuapl.edu/ NASA's Pluto-Kuiper Belt Mission] - launching in early 2006.
- [http://www.sfsite.com/~silverag/pluto.html Pluto in Science Fiction] - Bibliography of science fiction which is set on Pluto.
- [http://www.expreso.co.cr/centaurs/astronom/crossings/Plutocross.html Pluto/Neptune crossings]
- [http://space.com/scienceastronomy/051031_pluto_moons.html Space.co

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