1. A Brief History of Planetary Science Astronomy 311 Professor Lee Carkner Lecture 2

2. Ancient Astronomy  Ancient people had a much better view of the sky than we do today  They noticed that some things moved with respect to the stars:     Also transient things like comets and meteors

3. Caracol

4. Ancient Observing  People all over the world built devices to help observe the sky  Two basic purposes:  Calendars   Religious or Mystical Reasons    Our place in the universe has deep spiritual significance

5. Ancient Greek Astronomy  Greeks used reason and mathematics to study the sky  Greek discoveries:     Earth’s diameter

6. Finding the Size of the Earth Sunlight To Zenith Syene Alexandria To Sun 77 77

7. Eratosthenes’s Experiment Measure length of shadow, find angle between Sun and zenith: arctan (L/H) =   Subtract angles measured at both cities:  =  1 -  2 If D is distance between the two cities (756km), the circumference of the Earth is: C=(360/  ) X D zenith L=length of shadow Sun H = height of stick Angle = 

8. Geocentric Solar System  Earth is at center of Solar System    Developed between ~200BC (Hipparchus) and ~200AD (Ptolemy)

9. Retrograde Motion and Epicycles

10. Heliocentric Solar System  Sun at center of Solar System  First proposed by Aristarchus (~300BC)   More comprehensive model developed by Copernicus (~1500 AD) 

11. Uraniborg

12. Tycho, Kepler and the Motions of the Planets  Tycho Brahe carefully observed the planets for 20 years at Uraniborg (1576- 1597 AD)   Planets move in elliptical orbits and follow mathematical laws 

13. Galileo’s Observations

14. Galileo and the Telescope  Made many important observations starting in 1610, including:      Galileo’s writings were condemned by the church, but presented hard evidence  Careful observation and theorizing by Copernicus, Brahe, Kepler and Galileo disproved the seeming obvious and incontrovertible geocentric model.

15. Newton and Gravity  Why do the planets move?  Isaac Newton used Kepler’s Laws to discover gravity (~1700):   The universe is governed by universal rules

16. Discovering the Other Planets  Careful observation led to the discovery of:  Uranus (  Neptune (  Pluto (  No other large planets    Kuiper Belt objects detected in the 1990’s with large infrared telescopes confirm a large, well populated, “comet zone” beyond Pluto

17. Mare Imbrium - Apollo 15

18. The Grand Tour - Voyager II

19. Space Missions  A series of space missions since the early 1960’s have allowed close up views of the planets   This data has provided enormous insight into the history and nature of the solar system

20. Exoplanets

21. Extrasolar Planets  In the 1990’s first detection of planets outside of the solar system   Our solar system is not unique, billions of planets in the galaxy

22. Summary  Pre-civilized  Sun, moon and planets move  Can be used to determine seasons  Greek (~300BC -300AD)  It is possible to measure their properties  Copernican Revolution (~1500-1700AD)  Copernicus -- Planets (including the Earth) orbit the Sun  Kepler -- Planets have elliptical orbits and their motions are governed by laws  Galileo -- planets have features like the Earth (mountains, satellites)

23.  Newton and Physics (~1700 AD)  Planets follow laws of physics  Gravity accounts for orbital motion  Modern (20th Century)  Solar System consists of 9 planets plus cometary region  Space missions have allowed the detailed study of each planet  Planets exist around other stars

24. Next Time Meet in planetarium Read Chapter 1.1-1.5 Do homework