Lesson 1 How Greeks Knew that the Earth is Spherical.pptx
- 1. Objective: EXPLAIN HOW THE GREEKS KNEW THAT THE EARTH IS SPHERICAL
- 2. •Around 500 B.C., most Greeks believed that the Earth was round, not flat. •It was Pythagoras and his pupils who were first to propose a spherical Earth.
- 3. •In 500 to 430 B.C., Anaxagoras further supported Pythagoras' proposal through his observations of the shadows that the Earth cast on the Moon during a lunar eclipse.
- 4. •He observed that during a lunar eclipse, the Earth's shadow was reflected on the Moon's surface. The shadow reflected was circular.
- 5. •Around 340 B.C., Aristotle listed several arguments for a spherical Earth which included the positions of the North star, the shape of the Moon and the Sun, and the disappearance of the ships when they sail over the horizon.
- 6. •North Star The North Star was believed to be at a fixed position in the sky. However, when the Greeks traveled to places nearer the equator, like Egypt, they noticed that the North Star is closer to the horizon.
- 7. •The Shape of the Sun and the Moon Aristotle argued that if the Moon and the Sun were both spherical, then perhaps, the Earth was also spherical.
- 8. •Disappearing Ships If the Earth was flat, then a ship traveling away from an observer should become smaller and smaller until it disappeared.
- 9. •However, the Greeks observed that the ship became smaller and then its hull disappeared first before the sail as if it was being enveloped by the water until it completely disappeared.
- 10. The Size of the Spherical Earth •Ancient scholars tried to provide proof of a spherical Earth and its circumference through calculations. • It was Eratosthenes who gave the most accurate size during their time.
- 11. •While he was working at the Library of Alexandria in Northern Egypt, he received correspondence from Syene in Southern Egypt which stated that a vertical object did not cast any shadow at noontime during the summer solstice.
- 12. •But this was not the case in Alexandria where, at noon time during the summer solstice, a vertical object still casts a shadow.
- 13. • These observations could only mean that the Sun, during this time in Alexandria, was not directly overhead.
- 15. •Eratosthenes then determined the angle the Sun made with the vertical direction by measuring the shadow that a vertical stick cast. •He found out that in Alexandria, the Sun makes an angle of 7.2° from the vertical while 0° in Syene.
- 16. • To explain the difference, he hypothesized that the light rays coming from the sun are parallel, and the Earth is curved. •From his measurements, he computed the circumference of the Earth to be approximately 250 000 stadia (a stadium is a unit of measurement used to describe the size of a typical stadium at the time), about 40 000 kilometers.
- 18. •The following observations led the Greeks to conclude that the Earth is sphere: •The Earth casts a circular shadow on the Moon during a lunar eclipse. •The North Star has different positions depending on the location of the observer.
- 19. •The Moon and the Sun are both spherical. •A sailing ship becomes smaller and then its hull disappears first before the sail as if it is being enveloped by the water until it completely disappears. •The angle of the Sun with the vertical direction at noon time during a summer solstice varies from place to place.
- 21. •1. Which of the following is the shape of the Earth according to ancient Greeks? •A. cylinder •B. octagon •C. flat disc •D. sphere
- 22. •2. What is the shape of the Earth as described by modern astronomy? •A. ellipsoid •B. hyperboloid •C. oblate spheroid •D. oblate paraboloid
- 23. •3. Which of the following ancient Greek philosophers computed for the circumference of the Earth? •A. Anaxagoras •B. Pythagoras •C. Eratosthenes •D. Aristotle
- 24. •4. According to Erastothenes’ computations what is the circumference of the Earth? •A. 250 000 stadia •B. 500 stadia •C. 7.2 stadia •D. 40 000 stadia
- 25. •5. In which of the following is 250 000 stadia equal to? •A. 40 000 kilometers •B. 40 000 meters •C. 40 000 miles •D. 40 000 inches
- 26. •6. In which of the following events can the circular shadow of the Earth be observed most notably? •A. solar eclipse •B. lunar eclipse •C. summer solstice •D. winter solstice
- 27. •7. Which of the following describes the position of the North Star if you go towards the equator? •A. closer to the horizon •B. farther away from the horizon •C. The North Star is fixed wherever you are on the Earth. •D. It disappears completely.
- 28. •8. Which of the following can be observed of a cruising ship if the Earth is a flat disc? •A. It will shrink then only the sail will be visible until it completely disappears. •B. It will become bigger and bigger. •C. It will not change its size. •D. It will become smaller and smaller until it disappears.
- 29. •9. During which time did Eratosthenes observe the shadows cast by a vertical stick? •A. noon time in summer solstice •B. noon time in winter solstice •C. during a lunar eclipse •D. during a solar eclipse
- 30. • 10. According to Eratosthenes, which of the following explain why a vertical stick casts a shadow in Alexandria but not in Syene? • I. The Sun is directly overhead in Syene while in Alexandria, it is only almost directly overhead. • II. The light rays coming from the sun are parallel, and the Earth is curved. • III. The light rays coming from the sun are curved, and the Earth is flat. • IV. The Sun is directly overhead in Alexandria while in Syene, it is only almost directly overhead. • A. I only • B. I and II • C. III and IV • D. II and IV