The Shape of the World: The Mapping and Discovery of the Earth

"In centuries past, some thought the world was flat, or rested on the back of a turtle; for others, earth was a perfect sphere locked tightly into the heart of other spheres. But its true shape remained unseen by human eyes untikl christmas 1968, when the astronauts of Apollo 8 left the earth gravity to circumnavigate the moon. Then, planet earth became known to us all: a ghostly sphere..." The Shape of the World Late Antiquity Astronomy: The Hellenized Egyptian Capital, Alexandria developed 'New Mathematics' that enabled men to travel by land and overseas, measured the distance to the farthest stars, and estimated the number of sand grains in the universe. Alexandrine Astronomers were eventually able to measure by indirect means the radius of the earth, the diameter of the sun and moon and the distance to the moon, the sun, the planets, and the stars. Aristarchus virtually invented modern astronomy; while Euclid wrote the elements of geometry and founded mathematics, and methods of its instruction. "Alexandria originated the greatest advances of mathematics and along with them the creation of an earth-centered model of the orbits of the planets sound enough to survive ... for the very creator of a new solar system model, Claudius Ptolemy, who wrote ancient astronomy's most encyclopedic work, the Almagest*." Conversing With the Planets Ptolemy's Almagest is one of the most influential scientific works in history, second only to 'The Elements' by Euclid. A masterpiece of technical exposition, it was the basic textbook of astronomy for more than a thousand years, and still is the main source for our knowledge of ancient astronomy. It develops in a modern format, utilizing medieval Arabic translations to identify and make numerous corrections, adding extensive footnotes that take account of the great progress in understanding the work made in this century, due to the discovery of Babylonian records. Earth Mapping: Preparation of most except the largest scale maps, where a flat Earth can be assumed without significant error, demands accurate knowledge of the size and shape of the Earth. The notion that the Earth is spherical in shape was developed by the ancient Greeks. One of the earliest determinations of the size of the Earth, based on its perfect spherical; shape, was made by Eratosthenes the second century B.C. Alexandrian geographer and astronomer. He is noted for devising a system of latitude and longitude, and for being the first known to have calculated the circumference of the Earth. He also created a map of the world based on the available geographical knowledge of the era. He knew that at the summer solstice, the noon sun is directly overhead on the Tropic of Cancer, where the town of Syene (present-day Aswan, Egypt) was located since vertical shadows were cast there at the summer solstice. He also observed that at the summer solstice, angled shadows were cast at Alexandria which is located north of Syene on approximately the same me