Szydagis /10. Flammarion engraving (1888)

Transcription

1 Szydagis /10 Flammarion engraving (1888)

2 Pondering an Ultimate Question Originally domain of religion and philosophy alone, followed by science and religion mixing, then slowly A common theme of order from chaos seen in to explain the origins of the universe around us Babylonian myth: goddess of chaos killed by other gods and split in half, to create the heavens and the Earth of what happened in the beginning is one thing, but the ancients also considered the current setup India: animals support half-dome Earth. Egypt: mountains prop up sky Many ancient cultures studied the of the stars and the planets and came up with very accurate and tables, allowing them to predict exact dates of eclipses, sunrise and sunset, moonrise and moonset, the rising and selng of stars and loca@ons of planets within conjunc@ons -- without even having the correct model Astronomy also agriculture 2/10

3 The Aristotelian Universe Greeks get the credit as the first cosmologists in the West Aristotle, fourth century B.C., basing off work of Eudoxus Prime mover (creator) keeps the heavens (made of aether, the fiwh element) in perfect for all eternity. No space as we know it outside of them (meaningless) 8 solid crystal nested spheres ( most perfect shape) for Sun, Moon, 5 planets (Mercury, Venus, Mars, Jupiter, Saturn), fixed stars, around Earth with different rota@on direc@ons, speeds Heavens (non-empty) domain of unchanging perfec@on, while base Earth (made of earth, air, fire, water) subject to decay Circular mo@on in the sky, while straight or random on Earth. Natural state rest here, natural state movement up there. Earth itself neither rotates, nor revolves around anything, and is the natural place of earth-like par@cles; heaven adobe of aether Some modified version of this picture of the cosmos (sadly) held sway for over a millennium and a half in Europe 3/10

4 The Ptolemaic Universe Claudius Ptolemy, second century A.D. upon Aristotle s cosmological model S@ll geocentric (Earth = the center of the universe) Addressed anomalies like planet course paths, observed changes in brightness with extra circles (epicycles) Earth already known to be round (since ~ 500 B.C. thanks to Pythagoras, but we don t know for sure) 4/10 pbs.org

5 Activity Explain every single proof that you can think of that the earth is round (specifically spherical) instead of flat Either ancient or more modern ALSO: come up with a way to es@mate its size. What are the possible sources of (systema@c) error for your technique? Some good answers Shadows and s@cks in different ci@es (next slide) View from high-up places, or airplanes: can see a lot View from outer space (rockets, probes, satellites) Appearance of ships on the horizon on water Round shadow of the Earth on the Moon during a lunar eclipse Changing constella@ons as you cross the equator Other planets (inside and outside of our solar system) ~spheres Existence of zones Center of gravity: consistent weight 5/10

6 The Earth s Circumference Worked out in between of Aristotle and Ptolemy by jack-of-all-trades Eratosthenes (third century B.C.) hkps:// (excerpt from the original Cosmos, with famed astronomer Carl Sagan) Correc@on: we know today not sphere but spheroid (rota@on squishes the Earth, which is bulging at the equator) The Greeks did not just philosophize (a stereotype). They actually also made empirical measurements They also es@mated the sizes of the other planets and the Sun and Moon, and their distances from the Earth, but they lacked precision instruments, so missed by orders of magnitude, but had good qualita@ve ideas But they figured shapes out: for instance, full moon always looks like a circle, so must be sphere not disk 6/10

7 Library of ancient Alexandria 7/10 Eratosthenes

8 The Medieval Worldview Earth at center of everything theologically sensible for Church Though Hell and Devil at actual center Significant historical misunderstanding (Columbus cartoons): even the backwards people of the Middle Ages knew the earth wasn t flat for sure Greek (Aristotelian and Ptolemaic) cosmos 8/10 Dante, The Divine Comedy, mid-13 th century A.D.

9 Separation from Astrology Astronomy broke off from astrology (the two were once one) as the reasons behind the of the planets were largely due to Kepler (~1600) with his three laws of planetary and Newton s three laws, plus his (separate) law of gravity Astrology s@ll studied, but Same horoscope given to mul@ple people, but all agree fits them perfectly. Different horoscopes, but wrong signs. Same result. Horoscopes of brutal serial killers or other criminals given to ordinary people. Same result as above. Horoscopes vague, non-predic@ve. Moreover, twins can have very different lives. Only 12 signs of zodiac: so 1/12 of planet should have same or similar set of experiences every day (given daily horoscope) Horoscope will refer to big dividends or profits one day, for an Aquarius for instance, but tell that to an Aquarius dying of hunger in a third-world country Earth wobbles on its axis, so zodiac no longer even aligned Astrology ends with Saturn, because other planets not known in an@quity (Uranus, Neptune) 9/10

10 Reading and Questions The thirteenth-century monarch King Alfonso ( the Learned ) of Cas@le is said to have remarked, upon being briefed on the Ptolemaic model, that if this was really how God had built the universe, he might have given Him some beker advice. - Timothy Ferris, Coming of Age in the Milky Way Quiz #20 for homework on our *next* topics Finis