Transcript Slide 1
Foundations of Astronomy The scientific method-winning or losing? •Geodorno Bruno •Warned to stop teaching “heretical” sun-centered solar system of Copernicus. •Failed to heed church warnings during inquisition… •Was burned at the stake for continuing to teach earth orbited the sun. Reasons for early interest Stars as navigational aids. Mediterranean traders could sail to correct latitude….Using north star as a guide then sail east or west at the same latitude until they spotted familiar landmarks. Altitude of Polaris Note: the altitude of Polaris above the horizon equals the observers latitude. Here is Polaris as seen from San Francisco, latitude 37 degrees. Astrological and religious beliefs We are connected to the stars The sun does appear in front of the zodiacal constellations Humans were a bit confused about the other details till recently! image from: http://www.kprf.ru/clipart/misc/astrology.jpg http://www.perceptions.couk.com/imgs/spin3.gif Precession of the Equinoxes • The Earth’s axis precesses (wobbles) like a top, once about every 26,000 years. • Precession changes the positions in the sky of the celestial poles and the equinoxes. Polaris won't always be the north star. The spring equinox, seen by ancient Greeks in Aries, moves westward and is now in Pisces! Need for a Calendar especially related to agriculture. When to Plant? When to Harvest? When to Migrate? The Nile Flood was an especially important, yearly event. The Search for Meaning… • With no street lights and no alarm clocks… • The Night sky was a great glowing question… • Who are we? (no answer yet?) • Why are we here (not clear on that one either…?) • Where are we? • Humans have been working on that one for a long time! Early Cosmology models of the relation between the Earth and Celestial bodies How to explain the observations? Why did some celestial objects move on the celestial sphere? Why did most celestial objects stay in their places? Retrograde Motion Like the Sun, planets usually appear to move eastward relative to the stars. But as we pass them by in our orbit, they move west relative to the stars for a few weeks or months. Noticeable over many nights; on a single night, a planet rises in east and sets in west… 29 Images of Mars taken one week apart (Tunc Tezel, apod060422) So How to Explain all this? Crystalline spheres centered on Earth? The “rationalists” of Greece Plato (428-348 BC) : Heavens were perfect and that the most perfect geometric object was the circle. Socrates (469-399 BC) —form and perfection Plato’s ideas derived from Socrates study of forms… image of "Plato" a Plate, from: http://www.vidrioyarte.com/proddos.htm Aristotle (384-322 BCE) Plato's student –founded Lyceum in Athens Private Tutor to Alexander the Great Aristotle's interest didn’t end with astronomy! Image from: http://clendening.kumc.edu/dc/pc/Aristotle.jpg Aristotle Favored "Geo-Centric" model of the Universe. Why? Evidence and Logic! Observed no stellar parallaxes no winds spinning Earth would hurl its inhabitants into space. Had Pre Galilean/Newtonian view of Motion. Didn’t have “privileged” view of Earth Parallax Angle Apparent shift of a star’s position due to the Earth’s orbiting of the Sun The nearest stars are much farther away than the Greeks thought. So the parallax angles of the star are so small, that you need a telescope to observe them. Aristotle got some things correct! •demonstrated that the Earth was spherical: •Earth's shadow on the moon was always circular Practice Quiz 1. Who was the only astronomer executed for teaching what he believed was true? 2. What did he teach? 3. For a person traveling the globe, what does the altitude of Polaris tell them? 4. List two other reasons why ancient people were interested in the motions of the stars and planets Practice Quiz continued 5. What is the term describing the apparent “backward” motion of a planet on the celestial sphere? Draw a picture illustrating this phenomena. 6. Describe in one sentence what shapes Plato favored for describing orbital motion and why he favored them 7. List Three things Aristotle is famous for Practice Quiz-last page! 8. List one reason why Aristotle favored a geocentric model—explain his reasoning in one sentence 9. List another reason why Aristotle favored a geocentric model—explain his reasoning in one sentence 10. Describe one thing Aristotle was correct about! Quiz answers 1. Who was the only astronomer executed for teaching what he believed was true? Geodorno Bruno 2. What did he teach? The Heliocentric Model (Helios = sun) 3. For a person traveling the globe, what does the altitude of Polaris tell them? Their latitude! 4. List two other reasons why ancient people were interested in the motions of the stars and planets Navigation, As a calendar for Agriculture, Astrology, Religion Answers continued 5. What is the term describing the apparent “backward” motion of a planet on the celestial sphere? Draw a picture illustrating this phenomena. Retrograde motion 6. Describe in one sentence what shapes Plato favored for describing orbital motion and why he favored them. Regular geometric solids (platonic solids), especially the sphere because heavens are perfect, and the higher the symmetry, the more perfect a shape is. (…wait till you meet Kepler) 7. List things Aristotle is famous for Theory of motion, bio-medicine, Geocentric Model (including epicycles), proof that the Earth is round, and many more… And more answers… 8. List one reason why Aristotle favored a geocentric model—explain his reasoning in one sentence: no parallax of stars, no winds, not flung off earth..didn’t have modern concept of inertia, gravity, and distance to stars. 9. List another reason why Aristotle favored a geocentric model—explain his reasoning in one sentence..pick from above 10. Describe one thing Aristotle was correct about! Demonstrated that the Earth was round by shadow on Moon during eclipse.