CABL Forum - Re: Round Earth

Early life
Main article: Origin theories of Christopher Columbus
It is generally, although not universally, agreed that Christopher Columbus was born between August 25, and October 31, 1451 in Genoa, part of modern Italy.[4] His father was Domenico Colombo, a middle-class wool weaver, who later also had a cheese stand where Christopher was a helper, working both in Genoa and Savona. His mother was Susanna Fontanarossa. Bartolomeo, Giovanni Pellegrino and Giacomo were his brothers. Bartolomeo worked in a cartography workshop in Lisbon for at least part of his adulthood.[5]

Columbus never wrote any works in his native language, but it can be assumed this was the Genoese variety of Ligurian. In one of his writings, Columbus claims to have gone to the sea at the age of 10. In 1470 the Columbus family moved to Savona, where Domenico took over a tavern. In the same year, Columbus was on a Genoese ship hired in the service of René I of Anjou to support his attempt to conquer the Kingdom of Naples.

In 1473 Columbus began his apprenticeship as business agent for the important Centurione, Di Negro and Spinola families of Genoa. Later he allegedly made a trip to Chios, a Genoese colony in the Aegean Sea. In May 1476, he took part in an armed convoy sent by Genoa to carry a valuable cargo to northern Europe. He docked in Bristol, Galway, in Ireland and was possibly in Iceland in 1477. In 1479 Columbus reached his brother Bartolomeo in Lisbon, keeping on trading for the Centurione family. He married Filipa Moniz Perestrello, daughter of the Porto Santo governor, the Portuguese nobleman of Genoese origin Bartolomeu Perestrello. In 1479 or 1480, his son Diego was born.

Voyages
Main article: Voyages of Christopher Columbus

Navigation plans

The "Colombus map" was drawn circa 1490 in the workshop of Bartolomeo and Christopher Columbus in Lisbon.[6]
Columbus's geographical conceptions.Europe had long enjoyed a safe land passage to China and India— sources of valued goods such as silk, spices, and opiates— under the hegemony of the Mongol Empire (the Pax Mongolica, or Mongol peace). With the Fall of Constantinople to the Ottoman Turks in 1453, the land route to Asia became more difficult. In response to this the Columbus brothers had, by the 1480s, developed a plan to travel to the Indies, then construed roughly as all of south and east Asia, by sailing directly west across the "Ocean Sea," i.e., the Atlantic.

Washington Irving's 1828 biography of Columbus popularized the idea that Columbus had difficulty obtaining support for his plan because Europeans thought the Earth was flat.[7] In fact, the primitive maritime navigation of the time relied on the stars and the curvature of the spherical Earth. The knowledge that the Earth was spherical was widespread, and the means of calculating its diameter using an astrolabe was known to both scholars and navigators[8]. A spherical Earth had been the general opinion of Ancient Greek science, and this view continued through the Middle Ages (for example, Bede mentions it in The Reckoning of Time). In fact Eratosthenes had measured the diameter of the Earth with good precision in the second century BC.[9] Where Columbus did differ from the generally accepted view of his time is his (incorrect) arguments that assumed a significantly smaller diameter for the Earth, claiming that Asia could be easily reached by sailing west across the Atlantic. Most scholars accepted Ptolemy's correct assessment that the terrestrial landmass (for Europeans of the time, comprising Eurasia and Africa) occupied 180 degrees of the terrestrial sphere, and dismissed Columbus's claim that the Earth was much smaller, and that Asia was only a few thousand nautical miles to the west of Europe. Columbus's error was put down to his lack of experience in navigation at sea.[10]

Columbus believed the (incorrect) calculations of Marinus of Tyre, putting the landmass at 225 degrees, leaving only 135 degrees of water. Moreover, Columbus believed that one degree represented a shorter distance on the Earth's surface than was actually the case. Finally, he read maps as if the distances were calculated in Italian miles (1,238 meters). Accepting the length of a degree to be 56? miles, from the writings of Alfraganus, he therefore calculated the circumference of the Earth as 25,255 kilometers at most, and the distance from the Canary Islands to Japan as 3,000 Italian miles (3,700 km, or 2,300 statute miles). Columbus did not realize Al-Farghani used the much longer Arabic mile (about 1,830 m).

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