Ancient Astronomy.pptx
- 11. ANCIENT ASTRONOMY NORTH STAR -was believed to be at fixed position in the sky, however when the Greeks traveled to places nearer the equator, like Egypt, they noticed that it is closer to the horizon
- 12. ANCIENT ASTRONOMY Aristotle argued that if the Moon and the Sun were both spherical, then perhaps the Earth was the same
- 13. ANCIENT ASTRONOMY Disappearing ships - If the Earth was flat, then a ship traveling away from an observer should become smaller until it disappeared.. But the Greeks observed that the ship became smaller and its hull disappeared first before the sail.
- 14. Size of the spherical Earth ERATOSTHENES – gave the most accurate size during their time. Syene (Southern Egypt) and Alexandria : Vertical object shadow From his measurement: he computed the circumference of the Earth to be approx. 250,000 stadia, about 40,000 km
- 15. ANAXAGORAS ANAXAGORAS – was able to explain what causes the phases of the moon. To him, the moon shone only by reflected sunlight. Since it is a sphere, only half of it illuminated at a time and it changes periodically.
- 16. Eudoxus EUDOXUS – proposed a system of fixed spheres. He believed that the sun, moon and the five known planets and the stars were attached to these spheres which carried the heavenly bodies while they revolved around the stationary Earth.
- 17. ARISTOTLE ARISTOTLE – was a student of Plato. For him, the earth is spherical in shape since it always casts a curved shadow when it eclipses the moon. He also believed that the Earth was the center of the universe
- 18. ARISTARCHUS ARISTARCHUS – very first Greek to profess the heliocentric views “helio” – sun “centric”- centered
- 19. Eratosthenes ERATOSTHENES – the first successful attempt to determine the size of the Earth was made by him by applying geometric principles. -he observed that at the noonday sun in two Egyptian cities that were almost opposite each other – Syene (Aswan) in South and Alexandria in the North. He assumed they were in the same longitude.
- 20. Hipparchus HIPPARCHUS – is considered as the greatest of the early Greek astronomers who compared and observed the brightness of the 850 stars and arranged them into order of brightness or magnitude. -he also developed a method for predicting the times of lunar eclipses to within a few hours. -he also measure the length of the year to within the minutes of
- 21. CLAUDIUS PTOLEMY CLAUDIUS PTOLEMY – believed that the Earth was the center of the universe. His Ptolemic model claimed the planets moved in a complicated system of circles
- 23. PTOLEMIC MODEL The sun, moon and other planets move in circular orbits around the Earth. However, if observed night after night, these planets move slightly eastward among the stars. RETROGRADE MOTION – planets moves in the opposite direction for some time, after which it resume its eastward motion
- 24. ARISTOTLE’S CONCLUSION He lived in ancient Greece more than 300 yrs before the common era (BC). In those days, most people believed that many gods ruled the universe. He is regarded as the Father of Natural Science. His methods were basis for scientific method. He considered the position of the North Star He also observed that he could see the top of the sails first before the rest of the ship. (because of the
- 25. Thank You