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2 – A saga of mankind

2 – A saga of mankind. What do you know about the motion of the planets?. 1 – What is the shape of the Earth’s orbit around the Sun?. 2 – Do the planets orbit the Sun at constant speed?. 3 – Which planet has the largest orbital speed: Mercury or Jupiter?.

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2 – A saga of mankind

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  1. 2 – A saga of mankind

  2. What do you know about the motion of the planets?

  3. 1 – What is the shape of the Earth’s orbit around the Sun?

  4. 2 – Do the planets orbit the Sun at constant speed?

  5. 3 – Which planet has the largest orbital speed: Mercury or Jupiter?

  6. 4 – The Voyager spacecraft has now left the solar system. What force does it take to keep it moving in a straight line at constant speed?

  7. 5 – You bring your bathroom scale with you for a trip to the Moon. What does it display when you weigh yourself on the Moon?

  8. 6 – You drop amarble and a hammer from the top of the CN tower. Which reaches the ground first?

  9. 2-1 The birth of astronomy

  10. First astronomical record 30,000 BC: phases of the Moon carved on a bone Origin: Abri Blanchard, Perigord, France

  11. Picture yourself as an ancient farmer What is the evening show? What does your survival depend on? Weather and seasons One of the most important question farmers had to answer was: ‘What is today’s date?’ (When should I sow?)

  12. Religious ceremonies where often linked to astronomical events Winter solstice (shortest day of the year): people would gather and pray for the return of the warm season (Christmas Eve: 24th) Priests had to answer: “what is today’s date?” . They were often astronomers as well

  13. Calendars • Day (between two culminations of the Sun) The natural units for calendars are: • Month (from one full Moon to the next one) • Year (from one winter solstice to the next one) Challenges of the calendar: between 2 full moons: 29.5 days ≠ 30 between to winter solstice: 365.24 days ≠ 365

  14. Mesopotamia Irak (3000 – 100 BC)

  15. Where writing was invented

  16. Artist view of Babylon Next to Baghdad Ishtar gate

  17. The hanging garden of Babylon Babylonians believed that the planets and their motions influenced the fortune of kings and nations

  18. Very precise observations but never tried to explain what they saw Could forecast conjunctions and oppositions of planets Babylonian astronomers knew the approximate length of the year

  19. How could you measure the length of the year? Every day at noon, record the length of the shadow of a post June 21 March 21 ~ 183 days = half a year Dec 21

  20. Archeological site: Ziggurat, Ur

  21. Reconstruction of the temple/observatory Compass points Temples were built with specific places aligned to the heavens and based on the geometry of the land

  22. Astronomical records Letter reporting an eclipse

  23. Tablet library

  24. British Isles: Stonehenge Built from 2800 to 1500 BC

  25. People used stones to keep track of the motions of the Sun and Moon N O D D N O

  26. Egypt

  27. 3000 years ago, Egyptians adopted a calendar based on a 365-day year Senenmut calendar

  28. Egyptian map of the sky The ceilings of many royal tombs depict the night sky as groups of star-gods

  29. Egyptians knew that five bright objects, known today as “planets”, move from night to night against the background of the stars

  30. They portrayed the planets as deities sailing across the heavens in barques, and they were known as the "stars that know no rest".

  31. Sirius : brightest star of the night sky Each year, Sirius rose above horizon at dawn for ten days Egyptians kept careful track of the rising of Sirius to forecast the flooding of the Nile river Sirius in Canis Major

  32. Central America

  33. MAYA Ruins of the Caracol , Chichen Itza, Yutacan, Mexico 1000 years ago

  34. “Morning star”, “Evening star” = planet Venus Maya: Sophisticated calendar based on the motions of Venus

  35. You are lost on an isolated island in the Pacific ocean. How can you tell when is the shortest day of the year?

  36. Sept 21 March 21 June 21 Dec 21

  37. Aztecs Aztec calendars

  38. Incas Intihuatana, Machu Pichu Also used as a calendar

  39. Solar eclipses happen only once in a lifetime

  40. Polynesia Polynesians learned to navigate by the stars over hundred of kilometers It enabled them to colonize new islands

  41. The odds came from the sky (rain, storms, haze) so people associated motions in the sky to their fate Planets were symbols of gods that controlled human lives Weather, diseases, accidents, were thought to be whims of the gods Priests tried to understand what gods had in mind Many civilizations developed their own astrology. Position of the Sun, Moon and 5 visible planets determined the fate of humans

  42. Calvin’s opinion

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