By Ken Journigan Olympic High Astronomy-Renaissance

1. By Ken JourniganOlympic High Astronomy-Renaissance The History of Astronomy

2. Warm Up What is a geocentric model of the Universe? According to early astronomers, what did the Universe consist of ? Aristotle said that the cosmos was composed of five fundamental properties or elements. What were they? What did Aristotle think the shape of the Earth was? Why did he think that? Name three things that Hipparchus is known for?

3. Warm Up Name two discoveries made by Erastosthenes. What is an orrary? What is a heliocentric model of the Universe? What did Ptolemy include in his model of the Universe? What is an epicycle? How many epicycles did Ptolemy’s model include to work correctly?

4. Warm Up Who was Tycho Brahe? What did Tycho Brahe do? Who was Nicholas Copernicus and what did he propose? Who was Johann Kepler? Name and define his three laws.

5. Warm Up What is Newton’s 1st law of Universal motion? What is Newton’s 2nd law of Universal motion? What is Newton’s 3rd law of Universal motion? What is the mathematical formula for gravity?

6. Warm Up On Planet X, a pendulum swings 50 times in 60 seconds from a 30 cm string. What is the force of gravity on Planet X? On Planet Y, a pendulum swings 120 times in 60 seconds from a 40 cm string. What is the force of gravity on Planet Y?

7. Astronomical History A very complete story of astronomy is told in its history. The men and women of astronomical history are synonymous with the historical evolution of this observational science.

8. Geocentric vs. Heliocentric • http://www.astro.utoronto.ca/~zhu/ast210/both.html

9. Universal Models The Geocentric Model Supporters

10. The Geocentric Model of the Universe With one mere exception (to be named later), ancient astronomers placed the Earth at the center of the known Universe. This Universal Model was known as the Geocentric Model. “Geo” meaning Earth and “centric” meaning centered.

11. Aristotle (384 BC – March 7, 322 BC) Aristotle was an ancient Greekphilosopher, a student of Plato and teacher of Alexander the Great. Aristotle had a strong influence, and his teachings carried great weight. He promoted the geocentric model. According to Aristotle the cosmos were composed of five fundamental properties • Earth • Air • Water • Fire • The spherical shells of heavenly bodies with Earth at the center

12. Aristotle Aristotle believed that everything in the regions outside the Earth was perfect and eternally unchanging. All objects in the heavens were supposed to be perfect circles, except for stars, which were featureless points of light.

13. Celestial Sphere • http://www.mathpages.com/home/star3.htm

15. Warm Up • Give three examples of evidence of early astronomy! • The Universal model that places Earth at the center is called what? • Aristotle said that the cosmos was composed of five fundamental properties or elements. What were they? • What did Aristotle thing the shape of the Earth was? Why did he think that?

16. Aristotle Aristotle concluded that the Earth was round and not flat as some at the time believed. He based this on his observation of lunar ellipses where a portion of the Earth’s shadow falls on the moon.

17. Aristotle Aristotle’s beliefs about the geocentric model of the universe would pervade astronomy to such an extent, that they would not be challenged for another 1500 years. Plato and Aristotle

18. The Greek Astronomer Hipparchus Hipparcus (c. 190 BCE--c. 120 BCE) was born in Nicaea, a city in what is now Turkey. In the year 135 BCE, he was stargazing and saw a bright point of light he didn't recognize. This star appeared in the constellation Scorpio. It turned out to be a supernova. This disproved Aristotle’s idea of the perfect, unchanging Universe

19. The Greek Astronomer Hipparchus • Developed the first catalog of stars • Developed a magnitude scale where 1 represented the brightest stars and 6 represented the dimmest stars. • Determined the precession of Earth based on records from the past and compared it to his own observations

20. The Greek Astronomer Hipparchus Hipparcus cataloged the locations and brightness of over 850 stars. In addition, he calculated the length of the year to within seconds of its actual value and developed a system to predict eclipses to within hours.

21. Stellar Magnitude Hipparchus’ invented a system to identify how bright stars are. He placed all the stars he observed on a scale that he called “magnitude”. The brightest (magnitude 1) star was Sirius. Magnitude 6 stars were just barely visible. Each level of the magnitude scale represented a change in brightness of 2.5 times. A modified version of this system is still used. Magnitude 1 stars are 100 times brighter than magnitude 6 star.

22. The Greek Astronomer Hipparchus • Hipparchus had a problem making his star chart. It was easy enough to map the surface of the Earth, because the Earth has landmarks: rivers, mountains, cities--places of known location, to which other places can be compared. The sky, however, has no landmarks, just the stars themselves. Hipparchus decided to invent "landmarks" of his own. He picked one point in the sky and drew imaginary lines radiating out from it, like the spokes of a wheel. Then he drew circles around this central point which grew larger and larger.

23. The Greek Astronomer Hipparchus This made a grid around the sky, on which Hipparchus could locate any star he wanted. This idea soon improved Earthly map-making as well: the modern lines of longitude and latitude come directly from Hipparchus's method of mapping the sky. Instead of locating stars on the "celestial sphere" (the entire area visible around the Earth), later map-makers drew gridlines on their charts of the Earth's sphere.

24. Eratosthenes

25. Eratosthenes was born in Cyrene, Greece in 276 BC (now modern day Libya. Studying in Alexandria and Athenes, he was eventually appointed as chief librarian of the great Library of Alexandria. It was during this time that he built the famous armillary sphere as a model of the celestial sphere (until the later invention of the orrery) Eratosthenes

27. Orrery

28. Antikythera mechanism Many modern scholars believe that Eratosthenes was critical in the design on the Antikythera mechanism (orrery) due to his exclusive knowledge concerned the Earth’s relationship with the moon. Many consider it the first analog computer. It was part of the cargo discovered on a 2,500 year old roman sailing ship.

29. Recreation of the Antikythera mechanism

30. Eratosthenes and Size of the Earth About 250 BC, Eratosthenes used some of Aristotle's ideas to calculate the size of the Earth. On the summer solstice, observers at Syene, Egypt saw the sun directly overhead (the well). He also knew that in his hometown ofAlexandria, Egypt that the sun was at an angle of about 7.50 on that day. The angular displacement was measured. Using simple geometry, he calculated the distant from Syene to Alexandria represented 1/50 of a circle. Hiring someone to walk the distance to measure it 5,000 stadia, where each stadia equals about 700 m), he calculated that circumference of the Earth at around 252,000 stadia (or about 46,420 km). The result was within 1 percent accuracy of the figure known today.

31. Eratosthenes Eratosthenes was an athlete, poet, mathematician and astronomer. In addition to figuring our the Earth’s circumference he also calculated the tilt of the Earth’s axis and invented the leap day. He is likely the astronomer to first suggest the idea of the epicycle as well.

32. Warm Up • Name three innovative (new) things that Hipparchus did! • According to Hipparchus system to classify stars, what is the brightest star? • According to Hipparchus system to classify stars, what is the dimmest star? • What was Eratosthenes job in Alexandria? • What is he most famous for? • What is an armillary sphere? • What was the Antikythera mechanism?

33. Ptolemy When I trace at my pleasure the windings to and fro of the heavenly bodies, I no longer touch the earth with my feet: I stand in the presence of Zeus himself and take my fill of ambrosia, food of the gods.(studying the star sure makes me happy) Quoted in C B Boyer, A History of Mathematics (New York 1968)

34. Ptolemy Ptolemy’s full Latin name was Claudius Ptolemaeus (fl. AD 87-150, Alexandria), He was an ancient astronomer, geographer, and mathematician who considered the Earth the center of the universe (the "Ptolemaic system"). Virtually nothing is known about his life.

35. Ptolemy Claudius Ptolemy lived in Rome around 100 AD. His model of the solar system and heavenly sphere was a refinement of previous models developed by Greek astronomers. Ptolemy’s major contribution, however, was that his model could so accurately explain the motions of heavenly bodies, it became the model for understanding the structure of the solar system. Nearly all the early models, including Ptolemy’s version of the solar system, assumed that the Earth was the center of the Universe.

36. The Ptolemaic Model • The Ptolemaic model accounted for the apparent motions of the planets in a very direct way, by assuming that each planet moved on a small sphere or circle, called an epicycle, that moved on a larger sphere or circle, called a deferent. The stars, it was assumed, moved on a celestial sphere around the outside of the planetary spheres.

38. The Epicycle • http://physics.syr.edu/courses/java/demos/kennett/Epicycle/Epicycle.html • The idea of the epicycle was incorporating into Ptolemy’s universal model in order to explain retrograde motion

39. Prograde Versus Retrograde Motion • Prograde Motion: The regular west to east migration of celestial bodies across the sky. • Retrograde Motion: The irregular and periodic transit of planets across the sky from east to west.

40. Prograde Versus Retrograde Motion • http://jove.geol.niu.edu/faculty/stoddard/JAVA/luminaries.html

41. The Ptolemaic Model To accurately predict the motions of the heavens, Ptolemy used 80 epicycles to construct his model. The model was very accurate in predicting the motions of the heavens and therefore survived for around 1,400 years! Imagine what wrong ideas are around now that will last for that long!

42. Universal Models The Heliocentric Model Supporters

43. The Heliocentric Model • Heliocentric (sun-centered) model More accurately accounted for all observations of the movement of the sun and the moon, and the planets, and the stars • were good predictors of future positions of celestial bodies; models were verifiable • simplicity (Occam's Razor or the Principle of Parsimony) - as few assumptions or rules as possible; no contradictions.

44. Heliocentric Model Aristarchus of Samos, a Greek about 310-230 BC, had a heliocentric model. He proposed that all of the planets, including Earth revolved around the Sun, and that the Earth rotates on its axis once a day. His ideas did not gain widespread acceptance during his lifetime.

45. Aristarchus of Samos Aristarchus was the first person to give the solar system scale.

46. Nicholaus Copernicus/Mikolaj Kopernik

47. Nicholaus Copernicus Born in Trum, Poland, Copernicus was the youngest of four children. His father was a well to do merchant (copper trader), politician and civic leader. Following college and his fathers death, Copernicus went to live with his uncle who nominated him for a position as canon (a church official with a good salary and no work).

48. Copernicus was dissatisfied with the complexity of the geocentric model. In 1514 he anonymously published a hand-written document called the “Little Commentary” where he espoused and supported the idea of a heliocentric Universe. His beliefs would ultimately get him in trouble with the Church. Nicholaus Copernicus and the Revival of the Heliocentric Universe.

49. Nicholaus Copernicus and the Revival of the Heliocentric Universe. • His ideas included: • Sun is at the center of the universe, motionless; stars are motionless around the edge • Planets all revolve around the sun (6 total including Earth) • Moon revolves around Earth • Earth rotates on axis causing apparent daily motion of the heavens • Earth revolves around sun causing sun's annual movements • Retrograde motion of planets is due to relative planetary motions • Planetary orbits are perfect circles

50. Nicholaus Copernicus and the Revival of the Heliocentric Universe. Copernicus was the first to accurately determine the relative distances of the planets from the sun.