1. Major Changes in Astronomy Within last 400 years: -- Earth is not the center -- Universe is immense Within last 200 years: -- Appreciate the age of the universe Within the last 50 years: -- Universe is not static -- Contains truly bizarre objects Within the last 10 years: -- Many planets around other stars -- Water elsewhere in the solar system

2. History Aim: What was the study of Astronomy like long ago? Why did humans first study Astronomy? Mark time and cycles Predict season change for planting crops Navigation Curiosity… need to explain phenomena

3. Early Astronomy Earliest known records show astronomical interest. Many ancient cultures built sites and kept records on astronomical data. 3,000 BC - Stonehenge built (aligned with solstice and lunar eclipses).

6. Big Horn Medicine Wheel

7. Caracol Observatory - Mayans

9. Calendar Our calendar marks movements in our solar system. Year - one Earth revolution around Sun. Month - one Moon revolution around Earth Day - one Earth rotation

10. Early Philosophers Aristotle (350 BC) - Geocentric model. Why? Because it explained observations Geocentric Model: Earth at the center of universe. Everything revolves around Earth. Universe is unchanging and static.

12. Geocentric Model Observations it explains: -- The stars, sun, and planets appear to revolve around the Earth each day. -- Earth does not appear to move… no constant wind. -- No parallax.

13. Parallax How do we determine distances in space? Simple way is triangulation. If you know two angles and one side, trigonometry does the rest. Parallax = apparent movement of object when observer’s location moves.

14. Parallax

15. Early Philosophers Aristarchus of Samos (310- 230 BC) ** Earth and all planets orbit Sun. - idea rejected by later philosophers because they conflicted with Aristotle.

16. How Big? Eratosthenes - Greek mathematician (200 BC) Invented Latitude and Longitude. Measured Earth’s circumference.

17. Eratosthenes

18. How Round? Earth is an oblate spheroid.

19. Early Philosophers 3.Hipparchus - (150 BC) = -- first astronomer -- developed trigonometry -- first star chart -- discovered precession -- possibly developed the astrolabe

20. Precession Earth “wobbles” on its axis like a spinning top. Every 26,000 years Earth completes one wobble. Caused by Moon’s gravity.

22. Hipparchus Star Catalog

23. Farnese Globe

24. Astronomical Clock Antikythera Mechanism (150 BC) Made by Greeks 31 gears – give sun, moon, 5 planets, eclipses. As complex as a 19 th century clock.

25. Early Astronomers Claudius Ptolemy - (140) = Sophisticated geocentric model. -- made geocentrism the standard model. -- very complicated with 80 epicycles. -- explained Mars retrograde motion.

29. Early Astronomers Nicolaus Copernicus - (1473 – 1543) = Heliocentric Model --Sun is at the center of universe. -- Simple and elegant… no epicycles -- Not accepted until Galileo

31. Early Astronomers Tycho Brahe (1546 – 1601) = Measured movements of planets and stars. -- made most accurate star charts -- based ideas on actual observations -- Sun and Moon orbit Earth, but other planets orbit Sun.