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the Flat Earth

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Jason
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« on: June 25, 2007, 11:46:32 pm »

In Classical Antiquity

In early Classical Antiquity, the Earth was generally believed to be flat. Greek philosophers from that time period were prone to form conclusions similar to those of Anaximander, who believed the Earth to be a short cylinder with a flat, circular top.[2] It is conjectured that the first person to have advocated a spherical shape of the Earth was Pythagoras (6th century BC), but this idea is not supported by the fact that most presocratic Pythagoreans considered the world to be flat.[3] Eratosthenes, however, had already determined that the earth was a sphere and calculated its rough circumference by the third century B.C. [4]

By the time of Pliny the Elder in the 1st century, the Earth's spherical shape was generally acknowledged among the learned in the western world. Ptolemy derived his maps from a curved globe and developed the system of latitude, longitude, and climes. His writings remained the basis of European astronomy throughout the Middle Ages, although Late Antiquity and the Early Middle Ages (ca. 3rd to 7th centuries) saw occasional arguments in favor of a flat Earth.

The modern misconception that people of the Middle Ages believed that the Earth was flat first entered the popular imagination in the nineteenth century, thanks largely to the publication of Washington Irving's fantasy The Life and Voyages of Christopher Columbus in 1828.

By classical times an alternative idea, that Earth was spherical, had appeared in ancient India[5][6][7] and ancient Greece. Pythagoras, apparently on aesthetic grounds, held that all the celestial bodies were spherical. Aristotle provided observational evidence for the spherical Earth,[8] noting that travelers going south see southern constellations rise higher above the horizon. This is only possible if their horizon is at an angle to northerners' horizon. Thus the Earth's surface cannot be flat.[9] Also, the border of the shadow of Earth on the Moon during the partial phase of a lunar eclipse is always circular, no matter how high the Moon is over the horizon. Only a sphere casts a circular shadow in every direction, whereas a circular disk casts an elliptical shadow in most directions.[10]

The Earth's circumference was first determined around 240 BC by Eratosthenes. Eratosthenes knew that in Syene (now Aswan), in Egypt, the Sun was directly overhead at the summer solstice, while he estimated that a shadow cast by the Sun at Alexandria was 1/50th of a circle. He estimated the distance from Syene to Alexandria as 5,000 stades, and estimated the Earth's circumference was 250,000 stades and a degree was 700 stades (implying a circumference of 252,000 stades).[11] Eratosthenes used rough estimates and round numbers, but depending on the length of the stadion, his result is within a margin of between 2% and 20% of the actual circumference, 40,008 kilometres. Note that Eratosthenes could only measure the circumference of the Earth by assuming that the distance to the Sun is so great that the rays of sunlight are essentially parallel. A similar measurement, reported in a Chinese mathematical treatise, the Zhoubi suanjing (1st c. BC), was used to measure the distance to the Sun– albeit by assuming that the Earth was flat.

During this period, Earth was generally thought of as divided into zones of climate, with a frigid clime at the poles, a deadly torrid clime near the equator, and a mild and habitable temperate clime between the two. It was thought that the different temperatures of these zones were related with proximity to the sun. It was erroneously believed that no one could cross the torrid clime and reach the unknown lands on the other half of the globe. At the time, these imagined lands as well as their inhabitants were both called antipodes.[13]

Lucretius (1st. c. BC) opposed the concept of a spherical Earth, because he considered the idea of antipodes absurd. But by the 1st century AD, Pliny the Elder was in a position to claim that everyone agrees on the spherical shape of Earth (Natural History, 2.64), although there continued to be disputes regarding the nature of the antipodes, and how it is possible to keep the ocean in a curved shape. Interestingly, Pliny as an "intermediate" theory considers also the possibility of an imperfect sphere, "shaped like a pinecone". (Natural History, 2.65)

In the Second century the Alexandrian astronomer Ptolemy advanced many arguments for the sphericity of the Earth. Among them was the observation that when sailing towards mountains, they seem to rise from the sea, indicating that they were hidden by the curved surface of the sea.[14]

In late antiquity such widely read encyclopedists as Macrobius (4th c.) and Martianus Capella (5th c.) discussed the circumference of the sphere of the Earth, its central position in the universe, the difference of the seasons in northern and southern hemispheres, and many other geographical details.[15] In his commentary on Cicero's Dream of Scipio, Macrobius described the Earth as a globe of insignificant size in comparison to the remainder of the cosmos.

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