Mercury is the smallest and innermost planet in the Solar System. Its orbital period around the Sun of 87.97 days is the shortest of all the planets in the Solar System. It is named after the messenger of the gods. Like Venus, Mercury orbits the Sun within Earth's orbit as an inferior planet, never exceeds 28° away from the Sun when viewed from Earth; this proximity to the Sun means the planet can only be seen near the western or eastern horizon during the early evening or early morning. At this time it may appear as a bright star-like object, but is far more difficult to observe than Venus; the planet telescopically displays the complete range of phases, similar to Venus and the Moon, as it moves in its inner orbit relative to Earth, which reoccurs over the so-called synodic period every 116 days. Mercury is tidally locked with the Sun in a 3:2 spin-orbit resonance, rotates in a way, unique in the Solar System; as seen relative to the fixed stars, it rotates on its axis three times for every two revolutions it makes around the Sun.
As seen from the Sun, in a frame of reference that rotates with the orbital motion, it appears to rotate only once every two Mercurian years. An observer on Mercury would therefore see only one day every two Mercurian years. Mercury's axis has the smallest tilt of any of the Solar System's planets, its orbital eccentricity is the largest of all known planets in the Solar System. Mercury's surface appears cratered and is similar in appearance to the Moon's, indicating that it has been geologically inactive for billions of years. Having no atmosphere to retain heat, it has surface temperatures that vary diurnally more than on any other planet in the Solar System, ranging from 100 K at night to 700 K during the day across the equatorial regions; the polar regions are below 180 K. The planet has no known natural satellites. Two spacecraft have visited Mercury: Mariner 10 flew by in 1974 and 1975; the BepiColombo spacecraft is planned to arrive at Mercury in 2025. Mercury appears to have a solid silicate crust and mantle overlying a solid, iron sulfide outer core layer, a deeper liquid core layer, a solid inner core.
Mercury is one of four terrestrial planets in the Solar System, is a rocky body like Earth. It is the smallest planet in the Solar System, with an equatorial radius of 2,439.7 kilometres. Mercury is smaller—albeit more massive—than the largest natural satellites in the Solar System and Titan. Mercury consists of 70% metallic and 30% silicate material. Mercury's density is the second highest in the Solar System at 5.427 g/cm3, only less than Earth's density of 5.515 g/cm3. If the effect of gravitational compression were to be factored out from both planets, the materials of which Mercury is made would be denser than those of Earth, with an uncompressed density of 5.3 g/cm3 versus Earth's 4.4 g/cm3. Mercury's density can be used to infer details of its inner structure. Although Earth's high density results appreciably from gravitational compression at the core, Mercury is much smaller and its inner regions are not as compressed. Therefore, for it to have such a high density, its core must be rich in iron.
Geologists estimate. Research published in 2007 suggests. Surrounding the core is a 500–700 km mantle consisting of silicates. Based on data from the Mariner 10 mission and Earth-based observation, Mercury's crust is estimated to be 35 km thick.. One distinctive feature of Mercury's surface is the presence of numerous narrow ridges, extending up to several hundred kilometers in length, it is thought that these were formed as Mercury's core and mantle cooled and contracted at a time when the crust had solidified. Mercury's core has a higher iron content than that of any other major planet in the Solar System, several theories have been proposed to explain this; the most accepted theory is that Mercury had a metal–silicate ratio similar to common chondrite meteorites, thought to be typical of the Solar System's rocky matter, a mass 2.25 times its current mass. Early in the Solar System's history, Mercury may have been struck by a planetesimal of 1/6 that mass and several thousand kilometers across.
The impact would have stripped away much of the original crust and mantle, leaving the core behind as a major component. A similar process, known as the giant impact hypothesis, has been proposed to explain the formation of the Moon. Alternatively, Mercury may have formed from the solar nebula before the Sun's energy output had stabilized, it would have had twice its present mass, but as the protosun contracted, temperatures near Mercury could have been between 2,500 and 3,500 K and even as high as 10,000 K. Much of Mercury's surface rock could have been vaporized at such temperatures, forming an atmosphere of "rock vapor" that could have been carried away by the solar wind. A third hypothesis proposes that the solar nebula caused drag on the particles from which Mercury was accreting, which meant that lighter particles were lost from the accreting material and not gathered by Mercury; each hypothesis predicts a different surface composition, there are two space missions set to make observations.
The astronomical unit is a unit of length the distance from Earth to the Sun. However, that distance varies as Earth orbits the Sun, from a maximum to a minimum and back again once a year. Conceived as the average of Earth's aphelion and perihelion, since 2012 it has been defined as 149597870700 metres or about 150 million kilometres; the astronomical unit is used for measuring distances within the Solar System or around other stars. It is a fundamental component in the definition of another unit of astronomical length, the parsec. A variety of unit symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union used the symbol A to denote a length equal to the astronomical unit. In the astronomical literature, the symbol AU was common. In 2006, the International Bureau of Weights and Measures recommended ua as the symbol for the unit. In the non-normative Annex C to ISO 80000-3, the symbol of the astronomical unit is "ua". In 2012, the IAU, noting "that various symbols are presently in use for the astronomical unit", recommended the use of the symbol "au".
In the 2014 revision of the SI Brochure, the BIPM used the unit symbol "au". Earth's orbit around the Sun is an ellipse; the semi-major axis of this elliptic orbit is defined to be half of the straight line segment that joins the perihelion and aphelion. The centre of the Sun lies on this straight line segment, but not at its midpoint; because ellipses are well-understood shapes, measuring the points of its extremes defined the exact shape mathematically, made possible calculations for the entire orbit as well as predictions based on observation. In addition, it mapped out the largest straight-line distance that Earth traverses over the course of a year, defining times and places for observing the largest parallax in nearby stars. Knowing Earth's shift and a star's shift enabled the star's distance to be calculated, but all measurements are subject to some degree of error or uncertainty, the uncertainties in the length of the astronomical unit only increased uncertainties in the stellar distances.
Improvements in precision have always been a key to improving astronomical understanding. Throughout the twentieth century, measurements became precise and sophisticated, more dependent on accurate observation of the effects described by Einstein's theory of relativity and upon the mathematical tools it used. Improving measurements were continually checked and cross-checked by means of improved understanding of the laws of celestial mechanics, which govern the motions of objects in space; the expected positions and distances of objects at an established time are calculated from these laws, assembled into a collection of data called an ephemeris. NASA's Jet Propulsion Laboratory HORIZONS System provides one of several ephemeris computation services. In 1976, in order to establish a yet more precise measure for the astronomical unit, the IAU formally adopted a new definition. Although directly based on the then-best available observational measurements, the definition was recast in terms of the then-best mathematical derivations from celestial mechanics and planetary ephemerides.
It stated that "the astronomical unit of length is that length for which the Gaussian gravitational constant takes the value 0.01720209895 when the units of measurement are the astronomical units of length and time". Equivalently, by this definition, one AU is "the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass, moving with an angular frequency of 0.01720209895 radians per day". Subsequent explorations of the Solar System by space probes made it possible to obtain precise measurements of the relative positions of the inner planets and other objects by means of radar and telemetry; as with all radar measurements, these rely on measuring the time taken for photons to be reflected from an object. Because all photons move at the speed of light in vacuum, a fundamental constant of the universe, the distance of an object from the probe is calculated as the product of the speed of light and the measured time. However, for precision the calculations require adjustment for things such as the motions of the probe and object while the photons are transiting.
In addition, the measurement of the time itself must be translated to a standard scale that accounts for relativistic time dilation. Comparison of the ephemeris positions with time measurements expressed in the TDB scale leads to a value for the speed of light in astronomical units per day. By 2009, the IAU had updated its standard measures to reflect improvements, calculated the speed of light at 173.1446326847 AU/d. In 1983, the International Committee for Weights and Measures modified the International System of Units to make the metre defined as the distance travelled in a vacuum by light in 1/299792458 second; this replaced the previous definition, valid between 1960 and 1983, that the metre equalled a certain number of wavelengths of a certain emission line of krypton-86. The speed of light could be expressed as c0 = 299792458 m/s, a standard adopted by the IERS numerical standards. From this definition and the 2009 IAU standard, the time for light to traverse an AU is found to be
Transit of Venus
A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and a superior planet, becoming visible against the solar disk. During a transit, Venus can be seen from Earth as a small black dot moving across the face of the Sun; the duration of such transits is several hours. A transit is similar to a solar eclipse by the Moon. While the diameter of Venus is more than three times that of the Moon, Venus appears smaller, travels more across the face of the Sun, because it is much farther away from Earth. Transits of Venus are among the rarest of predictable astronomical phenomena, they occur in a pattern that repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years. The periodicity is a reflection of the fact that the orbital periods of Earth and Venus are close to 8:13 and 243:395 commensurabilities; the last transit of Venus was on 5 and 6 June 2012, was the last Venus transit of the 21st century.
The previous pair of transits were in December 1874 and December 1882. The next transits of Venus will take place on 10–11 December 2117, 8 December 2125. Venus transits are of great scientific importance as they were used to gain the first realistic estimates of the size of the Solar System. Observations of the 1639 transit, combined with the principle of parallax, provided an estimate of the distance between the Sun and the Earth, more accurate than any other up to that time; the 2012 transit provided scientists with a number of other research opportunities in the refinement of techniques to be used in the search for exoplanets. Venus, with an orbit inclined by 3.4° relative to the Earth's appears to pass under the Sun at inferior conjunction. A transit occurs when Venus reaches conjunction with the Sun at or near one of its nodes—the longitude where Venus passes through the Earth's orbital plane —and appears to pass directly across the Sun. Although the inclination between these two orbital planes is only 3.4°, Venus can be as far as 9.6° from the Sun when viewed from the Earth at inferior conjunction.
Since the angular diameter of the Sun is about half a degree, Venus may appear to pass above or below the Sun by more than 18 solar diameters during an ordinary conjunction. Sequences of transits repeat every 243 years. After this period of time Venus and Earth have returned to nearly the same point in their respective orbits. During the Earth's 243 sidereal orbital periods, which total 88,757.3 days, Venus completes 395 sidereal orbital periods of 224.701 days each, equal to 88,756.9 Earth days. This period of time corresponds to 152 synodic periods of Venus; the pattern of 105.5, 8, 121.5 and 8 years is not the only pattern, possible within the 243-year cycle, because of the slight mismatch between the times when the Earth and Venus arrive at the point of conjunction. Prior to 1518, the pattern of transits was 8, 113.5 and 121.5 years, the eight inter-transit gaps before the AD 546 transit were 121.5 years apart. The current pattern will continue until 2846, when it will be replaced by a pattern of 105.5, 129.5 and 8 years.
Thus, the 243-year cycle is stable, but the number of transits and their timing within the cycle will vary over time. Since the 243:395 Earth:Venus commensurability is only approximate, there are different sequences of transits occurring 243 years apart, each extending for several thousand years, which are replaced by other sequences. For instance, there is a series which ended in 541 BC, the series which includes 2117 only started in AD 1631. Ancient Indian, Egyptian and Chinese observers knew of Venus and recorded the planet's motions; the early Greek astronomers called Venus by two names—Hesperus the evening star and Phosphorus the morning star. Pythagoras is credited with realizing. There is no evidence. Venus was important to ancient American civilizations, in particular for the Maya, who called it Noh Ek, "the Great Star" or Xux Ek, "the Wasp Star". In the Dresden Codex, the Maya charted Venus's full cycle, but despite their precise knowledge of its course, there is no mention of a transit.
However, it has been proposed that frescoes found at Mayapan may contain a pictorial representation of the 12th or 13th century transits. The Persian polymath Avicenna claimed to have observed Venus as a spot on the Sun; this is possible, as there was a transit on May 24, 1032, but Avicenna did not give the date of his observation, modern scholars have questioned whether he could have observed the transit from his location at that time. He used his transit observation to help establish that Venus was, at least sometimes, below the Sun in Ptolemaic cosmology, i.e. the sphere of Venus comes before the sphere of the Sun when moving out from the Earth in the prevailing geocentric model. In 1627, Johannes Kepler became the first person to predict a transit of Venus, by predicting the 1631 event, his methods were not sufficiently accurate to predict that the transit would not be visible in most of Europe, as a consequence, nobody was able to use his prediction to observe the phenomenon. The first recorded observation of a transit of Venus was made by Jeremiah Horrocks from his home at Carr House in Much Hoole, near Preston in England, on 4 December 1639.
His friend, Will
Captain James Cook was a British explorer, navigator and captain in the Royal Navy. He made detailed maps of Newfoundland prior to making three voyages to the Pacific Ocean, during which he achieved the first recorded European contact with the eastern coastline of Australia and the Hawaiian Islands, the first recorded circumnavigation of New Zealand. Cook joined the British merchant navy as a teenager and joined the Royal Navy in 1755, he saw action in the Seven Years' War and subsequently surveyed and mapped much of the entrance to the Saint Lawrence River during the siege of Quebec, which brought him to the attention of the Admiralty and Royal Society. This acclaim came at a crucial moment in his career and the direction of British overseas exploration, led to his commission in 1766 as commander of HM Bark Endeavour for the first of three Pacific voyages. In three voyages, Cook sailed thousands of miles across uncharted areas of the globe, he mapped lands from New Zealand to Hawaii in the Pacific Ocean in greater detail and scale not charted by Western explorers.
As he progressed in his voyages of discovery, he surveyed and named features, recorded islands and coastlines on European maps for the first time. He displayed a combination of seamanship, superior surveying and cartographic skills, physical courage, an ability to lead men in adverse conditions. Cook was attacked and killed in 1779 during his third exploratory voyage in the Pacific while attempting to kidnap Hawaiian chief Kalaniʻōpuʻu in order to reclaim a cutter stolen from one of his ships, he left a legacy of scientific and geographical knowledge which influenced his successors well into the 20th century, numerous memorials worldwide have been dedicated to him. James Cook was born on 7 November 1728 in the village of Marton in Yorkshire and baptised on 14 November in the parish church of St Cuthbert, where his name can be seen in the church register, he was the second of eight children of James Cook, a Scottish farm labourer from Ednam in Roxburghshire, his locally born wife, Grace Pace, from Thornaby-on-Tees.
In 1736, his family moved to Airey Holme farm at Great Ayton, where his father's employer, Thomas Skottowe, paid for him to attend the local school. In 1741, after five years' schooling, he began work for his father, promoted to farm manager. Despite not being formally educated he became capable in mathematics and charting by the time of his Endeavour voyage. For leisure, he would climb Roseberry Topping, enjoying the opportunity for solitude. Cooks' Cottage, his parents' last home, which he is to have visited, is now in Melbourne, having been moved from England and reassembled, brick by brick, in 1934. In 1745, when he was 16, Cook moved 20 miles to the fishing village of Staithes, to be apprenticed as a shop boy to grocer and haberdasher William Sanderson. Historians have speculated that this is where Cook first felt the lure of the sea while gazing out of the shop window. After 18 months, not proving suited for shop work, Cook travelled to the nearby port town of Whitby to be introduced to friends of Sanderson's, John and Henry Walker.
The Walkers, who were Quakers, were prominent local ship-owners in the coal trade. Their house is now the Captain Cook Memorial Museum. Cook was taken on as a merchant navy apprentice in their small fleet of vessels, plying coal along the English coast, his first assignment was aboard the collier Freelove, he spent several years on this and various other coasters, sailing between the Tyne and London. As part of his apprenticeship, Cook applied himself to the study of algebra, trigonometry and astronomy—all skills he would need one day to command his own ship, his three-year apprenticeship completed, Cook began working on trading ships in the Baltic Sea. After passing his examinations in 1752, he soon progressed through the merchant navy ranks, starting with his promotion in that year to mate aboard the collier brig Friendship. In 1755, within a month of being offered command of this vessel, he volunteered for service in the Royal Navy, when Britain was re-arming for what was to become the Seven Years' War.
Despite the need to start back at the bottom of the naval hierarchy, Cook realised his career would advance more in military service and entered the Navy at Wapping on 17 June 1755. Cook married Elizabeth Batts, the daughter of Samuel Batts, keeper of the Bell Inn in Wapping and one of his mentors, on 21 December 1762 at St Margaret's Church, Essex; the couple had six children: James, Elizabeth, Joseph and Hugh. When not at sea, Cook lived in the East End of London, he attended St Paul's Church, where his son James was baptised. Cook has no direct descendants—all of his children died before having children of their own. Cook's first posting was with HMS Eagle, serving as able seaman and master's mate under Captain Joseph Hamar for his first year aboard, Captain Hugh Palliser thereafter. In October and November 1755, he took part in Eagle's capture of one French warship and the sinking of another, following which he was promoted to boatswain in addition to his other duties, his first temporary command was in March 1756 when he was master of Cruizer, a small cutter attached to Eagle while on patrol.
In June 1757 Cook formally passed his master's examinations at Trinity House, qualifying him to navigate and handle a ship of the King's fleet. He joined the frigate
The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process, it is by far the most important source of energy for life on Earth. Its diameter is about 1.39 million kilometers, or 109 times that of Earth, its mass is about 330,000 times that of Earth. It accounts for about 99.86% of the total mass of the Solar System. Three quarters of the Sun's mass consists of hydrogen; the Sun is a G-type main-sequence star based on its spectral class. As such, it is informally and not accurately referred to as a yellow dwarf, it formed 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into an orbiting disk that became the Solar System; the central mass became so hot and dense that it initiated nuclear fusion in its core. It is thought that all stars form by this process.
The Sun is middle-aged. It fuses about 600 million tons of hydrogen into helium every second, converting 4 million tons of matter into energy every second as a result; this energy, which can take between 10,000 and 170,000 years to escape from its core, is the source of the Sun's light and heat. In about 5 billion years, when hydrogen fusion in its core has diminished to the point at which the Sun is no longer in hydrostatic equilibrium, its core will undergo a marked increase in density and temperature while its outer layers expand to become a red giant, it is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury and Venus, render Earth uninhabitable. After this, it will shed its outer layers and become a dense type of cooling star known as a white dwarf, no longer produce energy by fusion, but still glow and give off heat from its previous fusion; the enormous effect of the Sun on Earth has been recognized since prehistoric times, the Sun has been regarded by some cultures as a deity.
The synodic rotation of Earth and its orbit around the Sun are the basis of solar calendars, one of, the predominant calendar in use today. The English proper name Sun may be related to south. Cognates to English sun appear in other Germanic languages, including Old Frisian sunne, Old Saxon sunna, Middle Dutch sonne, modern Dutch zon, Old High German sunna, modern German Sonne, Old Norse sunna, Gothic sunnō. All Germanic terms for the Sun stem from Proto-Germanic *sunnōn; the Latin name for the Sun, Sol, is not used in everyday English. Sol is used by planetary astronomers to refer to the duration of a solar day on another planet, such as Mars; the related word solar is the usual adjectival term used for the Sun, in terms such as solar day, solar eclipse, Solar System. A mean Earth solar day is 24 hours, whereas a mean Martian'sol' is 24 hours, 39 minutes, 35.244 seconds. The English weekday name Sunday stems from Old English and is a result of a Germanic interpretation of Latin dies solis, itself a translation of the Greek ἡμέρα ἡλίου.
The Sun is a G-type main-sequence star. The Sun has an absolute magnitude of +4.83, estimated to be brighter than about 85% of the stars in the Milky Way, most of which are red dwarfs. The Sun is heavy-element-rich, star; the formation of the Sun may have been triggered by shockwaves from more nearby supernovae. This is suggested by a high abundance of heavy elements in the Solar System, such as gold and uranium, relative to the abundances of these elements in so-called Population II, heavy-element-poor, stars; the heavy elements could most plausibly have been produced by endothermic nuclear reactions during a supernova, or by transmutation through neutron absorption within a massive second-generation star. The Sun is by far the brightest object in the Earth's sky, with an apparent magnitude of −26.74. This is about 13 billion times brighter than the next brightest star, which has an apparent magnitude of −1.46. The mean distance of the Sun's center to Earth's center is 1 astronomical unit, though the distance varies as Earth moves from perihelion in January to aphelion in July.
At this average distance, light travels from the Sun's horizon to Earth's horizon in about 8 minutes and 19 seconds, while light from the closest points of the Sun and Earth takes about two seconds less. The energy of this sunlight supports all life on Earth by photosynthesis, drives Earth's climate and weather; the Sun does not have a definite boundary, but its density decreases exponentially with increasing height above the photosphere. For the purpose of measurement, the Sun's radius is considered to be the distance from its center to the edge of the photosphere, the apparent visible surface of the Sun. By this measure, the Sun is a near-perfect sphere with an oblateness estimated at about 9 millionths, which means that its polar diameter differs from its equatorial diameter by only 10 kilometres; the tidal effect of the planets is weak and does not affect the shape of the Sun. The Sun rotates faster at its equator than at its poles; this differential rotation is caused by convective motion
The one-drop rule is a social and legal principle of racial classification, prominent in the United States in the 20th century. It asserted that any person with one ancestor of sub-Saharan African ancestry is considered black; this concept became codified into the law of some states in the early 20th century. It was associated with the principle of "invisible blackness" that developed after the long history of racial interaction in the South, as well as the hardening of slavery as a racial caste, it is an example of hypodescent, the automatic assignment of children of a mixed union between different socioeconomic or ethnic groups to the group with the lower status, regardless of proportion of ancestry in different groups. The legal concept of the "one-drop rule" does not exist outside the United States, it was never codified into federal law. Before and during the centuries of slavery, people had interracial relationships, both forced and voluntary. In the antebellum years, free people of mixed race were considered white if individuals had less than one-eighth or one-quarter African ancestry.
Many mixed-race people were absorbed into the majority culture based on appearance and carrying out community responsibilities. These and community acceptance were the more important factors if a person's racial status were questioned, not his or her documented ancestry; because of the social mobility of antebellum society in frontier areas, many people did not have documentation about their ancestors anyway. Based on late 20th -century DNA analysis and a preponderance of historical evidence, Thomas Jefferson is believed to have fathered the six mixed-race children with his slave Sally Hemings, herself three-quarters white. Four of these children, who were seven-eighths white, survived to adulthood. Hemings was a half-sister of Martha Wayles Jefferson, their children were born into slavery because of her status. Jefferson allowed the two oldest to escape in 1822. Three of the four entered white society as adults, all their descendants identified as white. Although racial segregation was adopted by southern states of the former Confederacy in the late 19th century, legislators resisted defining race by law as part of preventing interracial marriages.
In 1895 in South Carolina during discussion, George D. Tillman said, It is a scientific fact that there is not one full-blooded Caucasian on the floor of this convention; every member has in him a certain mixture of... colored blood... It would be a cruel injustice and the source of endless litigation, of scandal, horror and bloodshed to undertake to annul or forbid marriage for a remote obsolete trace of Negro blood; the doors would be open to scandal and greed. The one-drop rule was not adopted as law until the 20th century: first in Tennessee in 1910 and in Virginia under the Racial Integrity Act of 1924. In the early colonial years, children born of one Indigenous and one non-Native parent had a white father and an Indigenous mother; this was due to the majority of the early colonists being male. As many Native American tribes had matrilineal kinship systems, they considered the children to be born to the mother's family and clan. If they were raised in the culture, they were considered members of the community.
Among patrilineal tribes, such as the Omaha a child born to an Omaha mother and a white father could belong to the Omaha tribe only if the child were formally adopted into it by a male citizen. In contemporary practice, tribal laws around citizenship and parentage can vary between nations. In the U. S. the concept of the one-drop rule has been chiefly applied by white Americans to those of sub-Saharan black African ancestry in the 20th century, when the whites were trying to maintain white supremacy. The poet Langston Hughes wrote in his 1940 memoir: You see I am not black. There are lots of different kinds of blood in our family, but here in the United States, the word'Negro' is used to mean anyone who has any Negro blood at all in his veins. In Africa, the word is more pure, it means all Negro, therefore black. I am brown. Whites applied this rule to mixed-race descendants of Native American and African ethnicity, classifying them as African. In this they ignored; this distinction was critical. A child of a Native American mother should not be enslaved.
Today there are no enforceable laws in the U. S. in which the one-drop rule is applicable. Sociologically, the concept remains somewhat pervasive; some African Americans turned it around, claiming people of African descent in order to strengthen their political unity when working on activism for civil rights and legislation. Research has shown that some white people associate bi-racial children with the non-white ancestry of the individual. Both before and after the American Civil War, many people of mixed ancestry who "looked white" and were of white ancestry were absorbed into the white majority. State laws established differing standards. For instance, an 1822 Virginia law stated that to be defined as mulatto (tha
ArXiv is a repository of electronic preprints approved for posting after moderation, but not full peer review. It consists of scientific papers in the fields of mathematics, astronomy, electrical engineering, computer science, quantitative biology, mathematical finance and economics, which can be accessed online. In many fields of mathematics and physics all scientific papers are self-archived on the arXiv repository. Begun on August 14, 1991, arXiv.org passed the half-million-article milestone on October 3, 2008, had hit a million by the end of 2014. By October 2016 the submission rate had grown to more than 10,000 per month. ArXiv was made possible by the compact TeX file format, which allowed scientific papers to be transmitted over the Internet and rendered client-side. Around 1990, Joanne Cohn began emailing physics preprints to colleagues as TeX files, but the number of papers being sent soon filled mailboxes to capacity. Paul Ginsparg recognized the need for central storage, in August 1991 he created a central repository mailbox stored at the Los Alamos National Laboratory which could be accessed from any computer.
Additional modes of access were soon added: FTP in 1991, Gopher in 1992, the World Wide Web in 1993. The term e-print was adopted to describe the articles, it began as a physics archive, called the LANL preprint archive, but soon expanded to include astronomy, computer science, quantitative biology and, most statistics. Its original domain name was xxx.lanl.gov. Due to LANL's lack of interest in the expanding technology, in 2001 Ginsparg changed institutions to Cornell University and changed the name of the repository to arXiv.org. It is now hosted principally with eight mirrors around the world, its existence was one of the precipitating factors that led to the current movement in scientific publishing known as open access. Mathematicians and scientists upload their papers to arXiv.org for worldwide access and sometimes for reviews before they are published in peer-reviewed journals. Ginsparg was awarded a MacArthur Fellowship in 2002 for his establishment of arXiv; the annual budget for arXiv is $826,000 for 2013 to 2017, funded jointly by Cornell University Library, the Simons Foundation and annual fee income from member institutions.
This model arose in 2010, when Cornell sought to broaden the financial funding of the project by asking institutions to make annual voluntary contributions based on the amount of download usage by each institution. Each member institution pledges a five-year funding commitment to support arXiv. Based on institutional usage ranking, the annual fees are set in four tiers from $1,000 to $4,400. Cornell's goal is to raise at least $504,000 per year through membership fees generated by 220 institutions. In September 2011, Cornell University Library took overall administrative and financial responsibility for arXiv's operation and development. Ginsparg was quoted in the Chronicle of Higher Education as saying it "was supposed to be a three-hour tour, not a life sentence". However, Ginsparg remains on the arXiv Scientific Advisory Board and on the arXiv Physics Advisory Committee. Although arXiv is not peer reviewed, a collection of moderators for each area review the submissions; the lists of moderators for many sections of arXiv are publicly available, but moderators for most of the physics sections remain unlisted.
Additionally, an "endorsement" system was introduced in 2004 as part of an effort to ensure content is relevant and of interest to current research in the specified disciplines. Under the system, for categories that use it, an author must be endorsed by an established arXiv author before being allowed to submit papers to those categories. Endorsers are not asked to review the paper for errors, but to check whether the paper is appropriate for the intended subject area. New authors from recognized academic institutions receive automatic endorsement, which in practice means that they do not need to deal with the endorsement system at all. However, the endorsement system has attracted criticism for restricting scientific inquiry. A majority of the e-prints are submitted to journals for publication, but some work, including some influential papers, remain purely as e-prints and are never published in a peer-reviewed journal. A well-known example of the latter is an outline of a proof of Thurston's geometrization conjecture, including the Poincaré conjecture as a particular case, uploaded by Grigori Perelman in November 2002.
Perelman appears content to forgo the traditional peer-reviewed journal process, stating: "If anybody is interested in my way of solving the problem, it's all there – let them go and read about it". Despite this non-traditional method of publication, other mathematicians recognized this work by offering the Fields Medal and Clay Mathematics Millennium Prizes to Perelman, both of which he refused. Papers can be submitted in any of several formats, including LaTeX, PDF printed from a word processor other than TeX or LaTeX; the submission is rejected by the arXiv software if generating the final PDF file fails, if any image file is too large, or if the total size of the submission is too large. ArXiv now allows one to store and modify an incomplete submission, only finalize the submission when ready; the time stamp on the article is set. The standard access route is through one of several mirrors. Sev