Christopher Columbus Navigation Plans!

Navigation plans

The "Columbus map" was drawn circa 1490 in the workshop of Bartolomeo and Christopher Columbus in Lisbon.
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. 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,", 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. 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. The spherical view of the Earth had been the general opinion of Ancient Greek science, and continued as the standard view in the Middle Ages. In fact the Earth had generally been believed to be spherical since the 4th century BCE by most scholars and almost all navigators, and Eratosthenes had measured the diameter of the Earth with good precision in the second century BC. Columbus put forth arguments based on 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 occupied 180 degrees of the terrestrial sphere, and correctly 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.

Columbus believed the 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. 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 Columbus did not realize Al Farghani used the much longer Arabic mile.

The true circumference of the Earth is about 40,000 km, a figure established by Eratosthenes in the second century BC, and the distance from the Canary Islands to Japan 19,600 km. No ship that was readily available in the 15th century could carry enough food and fresh water for such a journey. Most European sailors and navigators concluded, likely correctly, that sailors undertaking a westward voyage from Europe to Asia non-stop would die of thirst or starvation long before reaching their destination. Spain, however, having completed an expensive war, was desperate for a competitive edge over other European countries in trade with the East Indies. Columbus promised such an advantage.

While Columbus's calculations underestimated the circumference of the Earth and the distance from the Canary Islands to Japan by the standards of his peers as well as in fact, Europeans generally assumed that the aquatic expanse between Europe and Asia was uninterrupted. Ultimately the discovery of the Americas, rather than the opening of trade with Asia, was to be Columbus' legacy.

There was a further element of key importance in the plans of Columbus, a closely held fact discovered by or otherwise learned by Columbus: the trade winds. A brisk wind from the east, commonly called an "easterly", propelled Santa Maria, La Nina, & La Pinta for 5 weeks from the Canaries. To return to Spain eastward against this prevailing wind would have required several months of an arduous sailing technique, called beating, during which food & drinkable water would have been utterly exhausted. Columbus returned home by following prevailing winds northeastward from the southern zone of the North Atlantic to the middle latitudes of the North Atlantic, where prevailing winds are eastward to the coastlines of Western Europe, where the winds curve southward towards the Iberian Peninsula. In fact, Columbus was wrong about degrees of longitude to be traversed and wrong about distance per degree, but he was right about a more vital fact: how to use the North Atlantic's great circular wind pattern, clockwise in direction, to get home.