THE EARTH'S SIZE AND SHAPE

Earth's size

The philosophers and savants in ancient civilizations could only speculate about the nature and shape of the world they lived in. The range of possible travel was limited and only simple instruments existed. Unrelated observations might have suggested that the Earth's surface was upwardly convex. For example, the Sun's rays continue to illuminate the sky and mountain peaks after its disk has already set, departing ships appear to sink slowly over the horizon, and the Earth's shadow can be seen to be curved during partial eclipse of the Moon. However, early ideas about the heavens and the Earth were intimately bound up with concepts of philosophy, religion and astrology. In Greek mythology the Earth was a disk-shaped region embracing the lands of the Mediterranean and surrounded by a circular stream, Oceanus, the origin of all the rivers. In the sixth century BC the Greek philosopher Anaximander visualized the heavens as a celestial sphere that surrounded a flat Earth at its center. Pythagoras (582–507 BC) and his followers were apparently the first to speculate that the Earth was a sphere. This idea was further propounded by the influential philosopher Aristotle (384–322 BC). Although he taught the scientific principle that theory must follow fact, Aristotle is responsible for the logical device called syllogism, which can explain correct observations by apparently logical accounts that are based on false premises.