Royal Observatory, Greenwich
The Royal Observatory, Greenwich is an observatory situated on a hill in Greenwich Park, overlooking the River Thames. It played a major role in the history of astronomy and navigation, is best known for the fact that the prime meridian passes through it, thereby gave its name to Greenwich Mean Time; the ROG has the IAU observatory code of the first in the list. ROG, the National Maritime Museum, the Queen's House and Cutty Sark are collectively designated Royal Museums Greenwich; the observatory was commissioned in 1675 by King Charles II, with the foundation stone being laid on 10 August. The site was chosen by Sir Christopher Wren. At that time the king created the position of Astronomer Royal, to serve as the director of the observatory and to "apply himself with the most exact care and diligence to the rectifying of the tables of the motions of the heavens, the places of the fixed stars, so as to find out the so much desired longitude of places for the perfecting of the art of navigation."
He appointed John Flamsteed as the first Astronomer Royal. The building was completed in the summer of 1676; the building was called "Flamsteed House", in reference to its first occupant. The scientific work of the observatory was relocated elsewhere in stages in the first half of the 20th century, the Greenwich site is now maintained exclusively as a museum, although the AMAT telescope became operational for astronomical research in 2018. 1675 – 22 June, Royal Observatory founded. 1675 – 10 August, construction began. 1714 Longitude Act established the Board of Longitude rewards. The Astronomer Royal was, until the Board was dissolved in 1828, always an ex officio Commissioner of Longitude. 1767 Astronomer Royal Nevil Maskelyne began publication of the Nautical Almanac, based on observations made at the Observatory. 1818 Oversight of the Royal Observatory was transferred from the Board of Ordnance to the Board of Admiralty. 1833 Daily time signals began. 1899 The New Physical Observatory was completed.
1924 Hourly time signals from the Royal Observatory were first broadcast on 5 February. 1948 Office of the Astronomer Royal was moved to Herstmonceux. 1957 Royal Observatory completed its move to Herstmonceux. The Greenwich site is renamed the Old Royal Observatory. 1990 RGO moved to Cambridge. 1998 RGO closed. Greenwich site is returned to its original name, the Royal Observatory, is made part of the National Maritime Museum. 2011 The Greenwich museums, including the ROG, become collectively the Royal Museums Greenwich. There had been significant buildings on this land since the reign of William I. Greenwich Palace, on the site of the present-day Maritime Museum, was the birthplace of both Henry VIII and his daughters Mary I and Elizabeth I. Greenwich Castle was a favourite place for Henry VIII to house his mistresses, so that he could travel from the Palace to see them; the establishment of a Royal Observatory was proposed in 1674 by Sir Jonas Moore who, in his role as Surveyor General at the Ordnance Office, persuaded King Charles II to create the observatory, with John Flamsteed installed as its director.
The Ordnance Office was given responsibility for building the Observatory, with Moore providing the key instruments and equipment for the observatory at his own personal cost. Flamsteed House, the original part of the Observatory, was designed by Sir Christopher Wren assisted by Robert Hooke, was the first purpose-built scientific research facility in Britain, it was built for a cost of £520 out of recycled materials on the foundations of Duke Humphrey's Tower, the forerunner of Greenwich Castle, which resulted in the alignment being 13 degrees away from true North, somewhat to Flamsteed's chagrin. The original observatory at first housed the scientific instruments to be used by Flamsteed in his work on stellar tables, over time incorporated additional responsibilities such as marking the official time of day, housing Her Majesty's Nautical Almanac Office. Moore donated two clocks, built by Thomas Tompion, which were installed in the 20 foot high Octagon Room, the principal room of the building.
They were of unusual design, each with a pendulum 13 feet in length mounted above the clock face, giving a period of four seconds and an accuracy unparalleled, of seven seconds per day. British astronomers have long used the Royal Observatory as a basis for measurement. Four separate meridians have passed through the buildings, defined by successive instruments; the basis of longitude, the meridian that passes through the Airy transit circle, first used in 1851, was adopted as the world's Prime Meridian at the International Meridian Conference on 22 October 1884. Subsequently, nations across the world used it as their standard for timekeeping; the Prime Meridian was marked by a brass strip in the Observatory's courtyard once the buildings became a museum in 1960, since 16 December 1999, has been marked by a powerful green laser shining north across the London night sky. Since the first triangulation of Great Britain in the period 1783–1853, Ordnance Survey maps have been based on an earlier version of the Greenwich meridian, defined by the transit instrument of James
England is a country, part of the United Kingdom. It shares land borders with Wales to Scotland to the north-northwest; the Irish Sea lies west of England and the Celtic Sea lies to the southwest. England is separated from continental Europe by the North Sea to the east and the English Channel to the south; the country covers five-eighths of the island of Great Britain, which lies in the North Atlantic, includes over 100 smaller islands, such as the Isles of Scilly and the Isle of Wight. The area now called England was first inhabited by modern humans during the Upper Palaeolithic period, but takes its name from the Angles, a Germanic tribe deriving its name from the Anglia peninsula, who settled during the 5th and 6th centuries. England became a unified state in the 10th century, since the Age of Discovery, which began during the 15th century, has had a significant cultural and legal impact on the wider world; the English language, the Anglican Church, English law – the basis for the common law legal systems of many other countries around the world – developed in England, the country's parliamentary system of government has been adopted by other nations.
The Industrial Revolution began in 18th-century England, transforming its society into the world's first industrialised nation. England's terrain is chiefly low hills and plains in central and southern England. However, there is upland and mountainous terrain in the west; the capital is London, which has the largest metropolitan area in both the United Kingdom and the European Union. England's population of over 55 million comprises 84% of the population of the United Kingdom concentrated around London, the South East, conurbations in the Midlands, the North West, the North East, Yorkshire, which each developed as major industrial regions during the 19th century; the Kingdom of England – which after 1535 included Wales – ceased being a separate sovereign state on 1 May 1707, when the Acts of Union put into effect the terms agreed in the Treaty of Union the previous year, resulting in a political union with the Kingdom of Scotland to create the Kingdom of Great Britain. In 1801, Great Britain was united with the Kingdom of Ireland to become the United Kingdom of Great Britain and Ireland.
In 1922 the Irish Free State seceded from the United Kingdom, leading to the latter being renamed the United Kingdom of Great Britain and Northern Ireland. The name "England" is derived from the Old English name Englaland, which means "land of the Angles"; the Angles were one of the Germanic tribes that settled in Great Britain during the Early Middle Ages. The Angles came from the Anglia peninsula in the Bay of Kiel area of the Baltic Sea; the earliest recorded use of the term, as "Engla londe", is in the late-ninth-century translation into Old English of Bede's Ecclesiastical History of the English People. The term was used in a different sense to the modern one, meaning "the land inhabited by the English", it included English people in what is now south-east Scotland but was part of the English kingdom of Northumbria; the Anglo-Saxon Chronicle recorded that the Domesday Book of 1086 covered the whole of England, meaning the English kingdom, but a few years the Chronicle stated that King Malcolm III went "out of Scotlande into Lothian in Englaland", thus using it in the more ancient sense.
According to the Oxford English Dictionary, its modern spelling was first used in 1538. The earliest attested reference to the Angles occurs in the 1st-century work by Tacitus, Germania, in which the Latin word Anglii is used; the etymology of the tribal name itself is disputed by scholars. How and why a term derived from the name of a tribe, less significant than others, such as the Saxons, came to be used for the entire country and its people is not known, but it seems this is related to the custom of calling the Germanic people in Britain Angli Saxones or English Saxons to distinguish them from continental Saxons of Old Saxony between the Weser and Eider rivers in Northern Germany. In Scottish Gaelic, another language which developed on the island of Great Britain, the Saxon tribe gave their name to the word for England. An alternative name for England is Albion; the name Albion referred to the entire island of Great Britain. The nominally earliest record of the name appears in the Aristotelian Corpus the 4th-century BC De Mundo: "Beyond the Pillars of Hercules is the ocean that flows round the earth.
In it are two large islands called Britannia. But modern scholarly consensus ascribes De Mundo not to Aristotle but to Pseudo-Aristotle, i.e. it was written in the Graeco-Roman period or afterwards. The word Albion or insula Albionum has two possible origins, it either derives from a cognate of the Latin albus meaning white, a reference to the white cliffs of Dover or from the phrase the "island of the Albiones" in the now lost Massaliote Periplus, attested through Avienus' Ora Maritima to which the former served as a source. Albion is now applied to England in a more poetic capacity. Another romantic name for England is Loegria, related to the Welsh word for England and made popular by its use in Arthurian legend; the earliest known evidence of human presence in the area now known as England was that of Homo antecessor, dating to approximate
Washington, D. C. formally the District of Columbia and referred to as Washington or D. C. is the capital of the United States. Founded after the American Revolution as the seat of government of the newly independent country, Washington was named after George Washington, first President of the United States and Founding Father; as the seat of the United States federal government and several international organizations, Washington is an important world political capital. The city is one of the most visited cities in the world, with more than 20 million tourists annually; the signing of the Residence Act on July 16, 1790, approved the creation of a capital district located along the Potomac River on the country's East Coast. The U. S. Constitution provided for a federal district under the exclusive jurisdiction of the U. S. Congress, the District is therefore not a part of any state; the states of Maryland and Virginia each donated land to form the federal district, which included the pre-existing settlements of Georgetown and Alexandria.
The City of Washington was founded in 1791 to serve as the new national capital. In 1846, Congress returned the land ceded by Virginia. Washington had an estimated population of 702,455 as of July 2018, making it the 20th most populous city in the United States. Commuters from the surrounding Maryland and Virginia suburbs raise the city's daytime population to more than one million during the workweek. Washington's metropolitan area, the country's sixth largest, had a 2017 estimated population of 6.2 million residents. All three branches of the U. S. federal government are centered in the District: Congress and the U. S. Supreme Court. Washington is home to many national monuments, museums situated on or around the National Mall; the city hosts 177 foreign embassies as well as the headquarters of many international organizations, trade unions, non-profit, lobbying groups, professional associations, including the World Bank Group, the International Monetary Fund, the Organization of American States, AARP, the National Geographic Society, the Human Rights Campaign, the International Finance Corporation, the American Red Cross.
A locally elected mayor and a 13‑member council have governed the District since 1973. However, Congress may overturn local laws. D. C. residents elect a non-voting, at-large congressional delegate to the House of Representatives, but the District has no representation in the Senate. The District receives three electoral votes in presidential elections as permitted by the Twenty-third Amendment to the United States Constitution, ratified in 1961. Various tribes of the Algonquian-speaking Piscataway people inhabited the lands around the Potomac River when Europeans first visited the area in the early 17th century. One group known as the Nacotchtank maintained settlements around the Anacostia River within the present-day District of Columbia. Conflicts with European colonists and neighboring tribes forced the relocation of the Piscataway people, some of whom established a new settlement in 1699 near Point of Rocks, Maryland. In his Federalist No. 43, published January 23, 1788, James Madison argued that the new federal government would need authority over a national capital to provide for its own maintenance and safety.
Five years earlier, a band of unpaid soldiers besieged Congress while its members were meeting in Philadelphia. Known as the Pennsylvania Mutiny of 1783, the event emphasized the need for the national government not to rely on any state for its own security. Article One, Section Eight, of the Constitution permits the establishment of a "District as may, by cession of particular states, the acceptance of Congress, become the seat of the government of the United States". However, the Constitution does not specify a location for the capital. In what is now known as the Compromise of 1790, Alexander Hamilton, Thomas Jefferson came to an agreement that the federal government would pay each state's remaining Revolutionary War debts in exchange for establishing the new national capital in the southern United States. On July 9, 1790, Congress passed the Residence Act, which approved the creation of a national capital on the Potomac River; the exact location was to be selected by President George Washington, who signed the bill into law on July 16.
Formed from land donated by the states of Maryland and Virginia, the initial shape of the federal district was a square measuring 10 miles on each side, totaling 100 square miles. Two pre-existing settlements were included in the territory: the port of Georgetown, founded in 1751, the city of Alexandria, founded in 1749. During 1791–92, Andrew Ellicott and several assistants, including a free African American astronomer named Benjamin Banneker, surveyed the borders of the federal district and placed boundary stones at every mile point. Many of the stones are still standing. A new federal city was constructed on the north bank of the Potomac, to the east of Georgetown. On September 9, 1791, the three commissioners overseeing the capital's construction named the city in honor of President Washington; the federal district was named Columbia, a poetic name for the United States in use at that time. Congress held its first session in Washington on November 17, 1800. Congress passed the District of Columbia Organic Act of 1801 that organized the District and placed the entire territory under the exclusive control of the federal
A prime meridian is a meridian in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian form a great circle; this great circle divides e.g. Earth, into two hemispheres. If one uses directions of East and West from a defined prime meridian they can be called the Eastern Hemisphere and the Western Hemisphere. A prime meridian is arbitrary, unlike an equator, determined by the axis of rotation—and various conventions have been used or advocated in different regions and throughout history; the most used modern meridian is the IERS Reference Meridian. It is derived but deviates from the Greenwich Meridian, selected as an international standard in 1884; the notion of longitude was developed by the Greek Eratosthenes in Alexandria, Hipparchus in Rhodes, applied to a large number of cities by the geographer Strabo. But it was Ptolemy. Ptolemy used as his basis the "Fortunate Isles", a group of islands in the Atlantic which are associated with the Canary Islands, although his maps correspond more to the Cape Verde islands.
The main point is to be comfortably west of the western tip of Africa as negative numbers were not yet in use. His prime meridian corresponds to 18° 40' west of Winchester today. At that time the chief method of determining longitude was by using the reported times of lunar eclipses in different countries. Ptolemy's Geographia was first printed with maps at Bologna in 1477, many early globes in the 16th century followed his lead, but there was still a hope. Christopher Columbus reported that the compass pointed due north somewhere in mid-Atlantic, this fact was used in the important Treaty of Tordesillas of 1494 which settled the territorial dispute between Spain and Portugal over newly discovered lands; the Tordesillas line was settled at 370 leagues west of Cape Verde. This is shown in Diogo Ribeiro's 1529 map. São Miguel Island in the Azores was still used for the same reason as late as 1594 by Christopher Saxton, although by it had been shown that the zero magnetic deviation line did not follow a line of longitude.
In 1541, Mercator produced his famous 41 cm terrestrial globe and drew his prime meridian through Fuerteventura in the Canaries. His maps used the Azores, following the magnetic hypothesis, but by the time that Ortelius produced the first modern atlas in 1570, other islands such as Cape Verde were coming into use. In his atlas longitudes were counted from 0° to 360°, not 180°W to 180°E as is usual today; this practice was followed by navigators well into the 18th century. In 1634, Cardinal Richelieu used the westernmost island of the Canaries, Ferro, 19° 55' west of Paris, as the choice of meridian; the geographer Delisle decided to round this off to 20°, so that it became the meridian of Paris disguised. In the early 18th century the battle was on to improve the determination of longitude at sea, leading to the development of the marine chronometer by John Harrison, but it was the development of accurate star charts, principally by the first British Astronomer Royal, John Flamsteed between 1680 and 1719 and disseminated by his successor Edmund Halley, that enabled navigators to use the lunar method of determining longitude more using the octant developed by Thomas Godfrey and John Hadley.
Between 1765 and 1811, Nevil Maskelyne published 49 issues of the Nautical Almanac based on the meridian of the Royal Observatory, Greenwich. "Maskelyne's tables not only made the lunar method practicable, they made the Greenwich meridian the universal reference point. The French translations of the Nautical Almanac retained Maskelyne's calculations from Greenwich—in spite of the fact that every other table in the Connaissance des Temps considered the Paris meridian as the prime." In 1884, at the International Meridian Conference in Washington, D. C. 22 countries voted to adopt the Greenwich meridian as the prime meridian of the world. The French argued for a neutral line, mentioning the Azores and the Bering Strait, but abstained and continued to use the Paris meridian until 1911. In October 1884 the Greenwich Meridian was selected by delegates to the International Meridian Conference held in Washington, D. C. United States to be the common zero of longitude and standard of time reckoning throughout the world.
The modern prime meridian, the IERS Reference Meridian, is placed near this meridian and is the prime meridian that has the widest use. The modern prime meridian, based at the Royal Observatory, was established by Sir George Airy in 1851; the position of the Greenwich Meridian has been defined by the location of the Airy Transit Circle since the first observation was taken with it by Sir George Airy in 1851. Prior to that, it was defined by a succession of earlier transit instruments, the first of, acquired by the second Astronomer Royal, Edmond Halley in 1721, it was set up in the extreme north-west corner of the Observatory between Flamsteed House and the Western Summer House. This spot, now subsumed into Flamsteed House, is 43 metres to the west of the Airy Transit Circle, a distance equivalent to 0.15 seconds of time. It was Airy's transit circle, adopted in principle as the Prime Meridian of th
The Paris meridian is a meridian line running through the Paris Observatory in Paris, France – now longitude 2°20′14.03″ East. It was a long-standing rival to the Greenwich meridian as the prime meridian of the world; the Paris meridian arc or French meridian arc is the name of the meridian arc measured along the Paris meridian. The French meridian arc was important for French cartography, inasmuch as the triangulations of France began with the measurement of the French meridian arc. Moreover, the French meridian arc was important for geodesy as it was one of the meridian arcs which were measured in order to determine the figure of the Earth; the determination of the figure of the earth was a problem of the highest importance in astronomy, inasmuch as the diameter of the earth was the unit to which all celestial distances had to be referred. In the year 1634, France ruled by Louis XIII and Cardinal Richelieu decided that the Ferro meridian should be used as the reference on maps, since this island is the most western position of the Old World.
It was thought to be 20 degrees west of Paris. A French astronomer, Abbé Jean Picard, measured the length of a degree of latitude along the Paris meridian and computed from it the size of the Earth during 1668–1670. In 1666, Louis XIV of France had authorized the building of an observatory in Paris. On Midsummer's Day 1667, members of the Academy of Sciences traced the future building's outline on a plot outside town near the Port Royal abbey, with Paris meridian bisecting the site north-south. French cartographers would use it as their prime meridian for more than 200 years. Old maps from continental Europe have a common grid with Paris degrees at the top and Ferro degrees offset by 20 at the bottom. Louis Feuillée worked on this problem in 1724, it was found that the actual island of El Hierro itself is in fact 20° 31' west of Paris, but the Ferro meridian was still defined as 20 degrees west of Paris. Four generations of the Cassini family headed the Paris Observatory, they directed the surveys of France for over 100 years.
Between 1684 and 1718 Giovanni Domenico Cassini and Jacques Cassini, starting from Picard’s base, carried a triangulation northwards from Paris to Dunkirk and southwards from Paris to Collioure. They measured a base of 7246 toises near Perpignan, a somewhat shorter base near Dunkirk; the immediate inference from this was that, the degree diminishing with increasing latitude, the earth must be a prolate spheroid. This conclusion was opposed to the theoretical investigations of Newton and Huygens, accordingly the Academy of Sciences of Paris determined to apply a decisive test by the measurement of arcs at a great distance from each other—one in the neighbourhood of the equator, the other in a high latitude, thus arose the celebrated expeditions of the French academicians to the Equator and to Lapland, the latter directed by Pierre Louis Maupertuis. In 1740 was published in the Paris Mémoires an account, by Cassini de Thury, of a remeasurement by himself and Nicolas Louis de Lacaille of the meridian of Paris.
With a view to determine more the variation of the degree along the meridian, they divided the distance from Dunkirk to Collioure into four partial arcs of about two degrees each, by observing the latitude at five stations. The results obtained by Giovanni Domenico and Jacques Cassini were not confirmed, but, on the contrary, the length of the degree derived from these partial arcs showed on the whole an increase with an increasing latitude. Cesar-François Cassini de Thury completed the Cassini map, published by his son Cassini IV in 1790. Moreover, the Paris meridian was linked with international collaboration in metrology. Cesar-François Cassini de Thury expressed the project to extend the French geodetic network all around the world and to connect the Paris and Greenwich observatories. In 1783 the French Academy of Science presented his proposal to King George III; this led to the Paris and Greenwich observatories' connection by General William Roy and the first triangulation of Great Britain.
France and Great Britain surveys' connection was repeated by French astronomers and geodesists in 1787 by Cassini IV, in 1823-1825 by François Arago and in 1861-1862 by François Perrier. Between 1792 and 1798 Pierre Méchain and Jean-Baptiste Delambre surveyed the Paris meridian arc between Dunkirk and Barcelona, they extrapolated from this measurement the distance from the North Pole to the Equator, 5 130 740 toises. As the metre had to be equal to one ten-million of this distance, it was defined as 0,513074 toises or 443,2936 lignes of the Toise of Peru. In the early 19th century, the Paris meridian's arc was recalculated with greater precision between Shetland and the Balearic Islands by the astronomer François Arago, whose name now appears on the plaques or medallions tracing the route of the meridian through Paris. Biot and Arago published their work as a fourth volume following the three volumes of "Bases du système métrique décimal ou mesure de l'arc méridien compris entre les parallèles de Dunkerque et Barcelone" by Delambre and Méchain.
In the second half of the 19th century, Carlos Ibáñez e Ibáñez de Ibero directed the survey of Spain. From 1870 to 1894 the Paris meridan's arc was remeasured by Perrier and Bassot in France and Algeria. In 1879, Ibáñez de Ibero for Spain and François Perrier for France directed t
Mali the Republic of Mali, is a landlocked country in West Africa, a region geologically identified with the West African Craton. Mali is the eighth-largest country in Africa, with an area of just over 1,240,000 square kilometres; the population of Mali is 18 million. Its capital is Bamako; the sovereign state of Mali consists of eight regions and its borders on the north reach deep into the middle of the Sahara Desert, while the country's southern part, where the majority of inhabitants live, features the Niger and Senegal rivers. The country's economy centers on mining; some of Mali's prominent natural resources include gold, being the third largest producer of gold in the African continent, salt. Present-day Mali was once part of three West African empires that controlled trans-Saharan trade: the Ghana Empire, the Mali Empire, the Songhai Empire. During its golden age, there was a flourishing of mathematics, astronomy and art. At its peak in 1300, the Mali Empire covered an area about twice the size of modern-day France and stretched to the west coast of Africa.
In the late 19th century, during the Scramble for Africa, France seized control of Mali, making it a part of French Sudan. French Sudan joined with Senegal in 1959. Shortly thereafter, following Senegal's withdrawal from the federation, the Sudanese Republic declared itself the independent Republic of Mali. After a long period of one-party rule, a coup in 1991 led to the writing of a new constitution and the establishment of Mali as a democratic, multi-party state. In January 2012, an armed conflict broke out in northern Mali, in which Tuareg rebels took control of a territory in the north, in April declared the secession of a new state, Azawad; the conflict was complicated by a military coup that took place in March and fighting between Tuareg and rebels. In response to territorial gains, the French military launched Opération Serval in January 2013. A month Malian and French forces recaptured most of the north. Presidential elections were held on 28 July 2013, with a second-round run-off held on 11 August, legislative elections were held on 24 November and 15 December 2013.
The name Mali is taken from the name of the Mali Empire. The name was derived from the Mandinka or Bambara word mali, meaning "hippopotamus", but it came to mean "the place where the king lives"; the word carries the connotation of strength. Guinean writer Djibril Niane suggests in Sundiata: An Epic of Old Mali that it is not impossible that Mali was the name given to one of the capitals of the emperors. 14th-century Moroccan traveler Ibn Battuta reported that the capital of the Mali Empire was called Mali. One Mandinka tradition tells that the legendary first emperor Sundiata Keita changed himself into a hippopotamus upon his death in the Sankarani River, that it's possible to find villages in the area of this river, termed "old Mali", which have Mali for a name; this name could have been that of a city. In old Mali, there is one village called Malika which means "New Mali."Another theory suggests that Mali is a Fulani pronunciation of the name of the Mande peoples. It is suggested that a sound shift led to the change, whereby in Fulani the alveolar segment /nd/ shifts to /l/ and the terminal vowel denasalises and raises, thus "Manden" shifts to /Mali/.
Mali was once part of three famed West African empires which controlled trans-Saharan trade in gold, salt and other precious commodities. These Sahelian kingdoms had rigid ethnic identities; the earliest of these empires was the Ghana Empire, dominated by the Soninke, a Mande-speaking people. The empire expanded throughout West Africa from the 8th century until 1078, when it was conquered by the Almoravids; the Mali Empire formed on the upper Niger River, reached the height of power in the 14th century. Under the Mali Empire, the ancient cities of Djenné and Timbuktu were centers of both trade and Islamic learning; the empire declined as a result of internal intrigue being supplanted by the Songhai Empire. The Songhai people originated in current northwestern Nigeria; the Songhai had long been a major power in West Africa subject to the Mali Empire's rule. In the late 14th century, the Songhai gained independence from the Mali Empire and expanded subsuming the entire eastern portion of the Mali Empire.
The Songhai Empire's eventual collapse was the result of a Moroccan invasion in 1591, under the command of Judar Pasha. The fall of the Songhai Empire marked the end of the region's role as a trading crossroads. Following the establishment of sea routes by the European powers, the trans-Saharan trade routes lost significance. One of the worst famines in the region's recorded history occurred in the 18th century. According to John Iliffe, "The worst crises were in the 1680s, when famine extended from the Senegambian coast to the Upper Nile and'many sold themselves for slaves, only to get a sustenance', in 1738–1756, when West Africa's greatest recorded subsistence crisis, due to drought and locusts killed half the population of Timbuktu." Mali fell under the control of France during the late 19th century. By 1905, most of the area was under firm French control as a part of French Sudan. In early 1959, French Sudan and Senegal united to become the Mali Federation; the Mali Federation gained independence from France on 20 June 1960.
Senegal withdrew from the federation in August 1960, which allowed the Sudanes
President of the United States
The president of the United States is the head of state and head of government of the United States of America. The president directs the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces. In contemporary times, the president is looked upon as one of the world's most powerful political figures as the leader of the only remaining global superpower; the role includes responsibility for the world's most expensive military, which has the second largest nuclear arsenal. The president leads the nation with the largest economy by nominal GDP; the president possesses international hard and soft power. Article II of the Constitution establishes the executive branch of the federal government, it vests the executive power of the United States in the president. The power includes the execution and enforcement of federal law, alongside the responsibility of appointing federal executive, diplomatic and judicial officers, concluding treaties with foreign powers with the advice and consent of the Senate.
The president is further empowered to grant federal pardons and reprieves, to convene and adjourn either or both houses of Congress under extraordinary circumstances. The president directs the foreign and domestic policies of the United States, takes an active role in promoting his policy priorities to members of Congress. In addition, as part of the system of checks and balances, Article I, Section 7 of the Constitution gives the president the power to sign or veto federal legislation; the power of the presidency has grown since its formation, as has the power of the federal government as a whole. Through the Electoral College, registered voters indirectly elect the president and vice president to a four-year term; this is the only federal election in the United States, not decided by popular vote. Nine vice presidents became president by virtue of a president's intra-term resignation. Article II, Section 1, Clause 5 sets three qualifications for holding the presidency: natural-born U. S. citizenship.
The Twenty-second Amendment precludes any person from being elected president to a third term. In all, 44 individuals have served 45 presidencies spanning 57 full four-year terms. Grover Cleveland served two non-consecutive terms, so he is counted twice, as both the 22nd and 24th president. Donald Trump of New York is the current president of the United States, he assumed office on January 20, 2017. In July 1776, during the American Revolutionary War, the Thirteen Colonies, acting jointly through the Second Continental Congress, declared themselves to be 13 independent sovereign states, no longer under British rule. Recognizing the necessity of coordinating their efforts against the British, the Continental Congress began the process of drafting a constitution that would bind the states together. There were long debates on a number of issues, including representation and voting, the exact powers to be given the central government. Congress finished work on the Articles of Confederation to establish a perpetual union between the states in November 1777 and sent it to the states for ratification.
Under the Articles, which took effect on March 1, 1781, the Congress of the Confederation was a central political authority without any legislative power. It could make its own resolutions and regulations, but not any laws, could not impose any taxes or enforce local commercial regulations upon its citizens; this institutional design reflected how Americans believed the deposed British system of Crown and Parliament ought to have functioned with respect to the royal dominion: a superintending body for matters that concerned the entire empire. The states were out from under any monarchy and assigned some royal prerogatives to Congress; the members of Congress elected a President of the United States in Congress Assembled to preside over its deliberation as a neutral discussion moderator. Unrelated to and quite dissimilar from the office of President of the United States, it was a ceremonial position without much influence. In 1783, the Treaty of Paris secured independence for each of the former colonies.
With peace at hand, the states each turned toward their own internal affairs. By 1786, Americans found their continental borders besieged and weak and their respective economies in crises as neighboring states agitated trade rivalries with one another, they witnessed their hard currency pouring into foreign markets to pay for imports, their Mediterranean commerce preyed upon by North African pirates, their foreign-financed Revolutionary War debts unpaid and accruing interest. Civil and political unrest loomed. Following the successful resolution of commercial and fishing disputes between Virginia and Maryland at the Mount Vernon Conference in 1785, Virginia called for a trade conference between all the states, set for September 1786 in Annapolis, with an aim toward resolving further-reaching interstate commercial antagonisms; when the convention failed for lack of attendance due to suspicions among most of the other states, Alexander Hamilton led the Annapolis delegates in a call for a convention to offer revisions to the Articles, to be held the next spring in Philadelphia.
Prospects for the next convention appeared bleak until James Madison and Edmund Randolph succeeded in securing George Washington's attendance to Philadelphia as a delegate for Virginia. When the Constitutional Convention convened in May 1787, the 12 state delegations in attendance (Rh