1. History of Astronomy How have ideas about the solar system and our place in it changed?

2. Egyptians Saw patterns in the Sun, moon, and Venus Saw patterns in the Sun, moon, and Venus Called the sun “Ra” (Sun god) – rode in his boat across the sky daily Called the sun “Ra” (Sun god) – rode in his boat across the sky daily Developed 365 day year solar calendar Developed 365 day year solar calendar

3. Ra (on right)

4. Greece Eudoxus, born 400 B.C. Eudoxus, born 400 B.C. saw objects that moved in sky saw objects that moved in sky called planets, sun, and moon “wanderers” called planets, sun, and moon “wanderers” Earth motionless and at the center of universe Earth motionless and at the center of universe Ptolemy, AD 140 Ptolemy, AD 140 Leading astronomer Leading astronomer “geocentric” theory – is center of universe. Lasted for 1400 years. “geocentric” theory – earth is center of universe. Lasted for 1400 years.

5. Ptolemy “epicycles”

6. Arabs Caliph Harun-al-Rashid, ruler Caliph Harun-al-Rashid, ruler Scholars translated Greek texts into Arabic and preserved in “House of Wisdom” library – in Baghdad Scholars translated Greek texts into Arabic and preserved in “House of Wisdom” library – in Baghdad Measured positions of stars and planets with fine instruments, astrolabe, can perform calculations Measured positions of stars and planets with fine instruments, astrolabe, can perform calculations Named the red giant Betelgeuse, in Orion Named the red giant Betelgeuse, in Orion 325 light years away 325 light years away

7. Betelgeuse – “shoulder” Orion constellation

8. Poland Copernicus – 1540 Copernicus – 1540 First to suggest “heliocentric model” – sun is center of universe First to suggest “heliocentric model” – sun is center of universe Objects orbit sun in perfect circles Objects orbit sun in perfect circles Still not a perfect model Still not a perfect model

9. Copernicus from book De Revolutionibus The English version…

10. What do you think? Why do you think it was difficult for people to accept a heliocentric model (sun centered) over the geocentric model (Earth centered)? Why do you think it was difficult for people to accept a heliocentric model (sun centered) over the geocentric model (Earth centered)? Geocentric modelHeliocentric model

11. Denmark Tycho Brahe – 1576 Tycho Brahe – 1576 Collected data of position of planets for 20 years Collected data of position of planets for 20 years Able to make accurate predictions of positions without telescopes Able to make accurate predictions of positions without telescopes Had own “Tychonic Universe” – combination of Ptolemy and Copernicus Had own “Tychonic Universe” – combination of Ptolemy and Copernicus Earth is stationary Earth is stationary Believed in circular orbits Believed in circular orbits

12. Tychonic Universe

13. Why the Circles? Why do you think these astronomers believed in circular orbits? Why do you think these astronomers believed in circular orbits?

14. Kepler Works with Tycho – after Tycho’s death, Tycho’s family sued to recover instruments and books of observations Works with Tycho – after Tycho’s death, Tycho’s family sued to recover instruments and books of observations Why? Why? Kepler was a Copernican, and they knew he wouldn’t follow the Tychonic system Kepler was a Copernican, and they knew he wouldn’t follow the Tychonic system Kepler kept the books! Began to study motion of Mars … Kepler kept the books! Began to study motion of Mars …

15. Kepler Elliptical orbits

16. Kepler’s First Law of Planetary Motion Orbits are elliptical (oval shaped), Orbits are elliptical (oval shaped), sun is at the focus sun is at the focus

17. Kepler’s Second Law of Planetary Motion A line from a planet to the sun sweeps over equal areas in equal times A line from a planet to the sun sweeps over equal areas in equal times Planets travel at different speeds – due to pull of gravity Planets travel at different speeds – due to pull of gravity Same time, moves slower Closer to Sun, moves faster… Why?

18. Kepler’s Unanswered Question What keeps planets in orbit? What keeps planets in orbit?

19. Galileo Galilei Born in 1564 Born in 1564 Supports Copericus’ theory of heliocentric universe Supports Copericus’ theory of heliocentric universe Used telescope to observe: Used telescope to observe: surface of Moon – was not perfect (like Ptolemaic model) surface of Moon – was not perfect (like Ptolemaic model) Phases of Venus Phases of Venus Milky Way was made up of many stars Milky Way was made up of many stars Moons of Jupiter Moons of Jupiter

20. Galileo Moon surface Phases of Venus

21. Isaac Newton Born in 1654 (year Galileo dies) Born in 1654 (year Galileo dies) Three Laws of Motion Three Laws of Motion Review from exam! Review from exam! These laws help us understand orbital motion These laws help us understand orbital motion 1 st law – 1 st law – 2 nd law – 2 nd law – 3 rd law – 3 rd law –

22. Newton answers Kepler’s Question… What keeps planets in orbit?

23. Tying it all up… Myths Myths See patterns See patterns Ptolemy Ptolemy Copernicus Copernicus Kepler Kepler Galileo Galileo Newton Newton

24. Homework Timeline – list at least four models of relationship between sun and planets. Timeline – list at least four models of relationship between sun and planets. Include: dates, astronomer, model Include: dates, astronomer, model Read – Chapter 16.1: pp. 526 – 530. Read – Chapter 16.1: pp. 526 – 530.