ASTRONOMY 202 Spring 2007: Solar System Exploratio n

Instructor: Dr. David Alexander Web-site: w ww.ruf.rice.edu/~dalex/ASTR202_S07

Class 7: The Science of Astronomy [1/29/07]

� Announcements

� Astronomy of the Ancients

� The Big Fat Greek Contribution• The ‘perfect’ Universe• Wheels upon wheels

� The Copernican Revolution• Putting the Sun in its place• Setting the scene

� Discussion & Questions?

Chapter 3Chapter 3

Announcements

�� Homework 2 due NOW Homework 2 due NOW

�� Homework 3 available online Homework 3 available online –– due Mon Feb 5due Mon Feb 5

Astronomy of the AncientsAstronomy of the Ancients

Big Horn Medicine Wheel

Templo Mayor, TenochtitlanAztec, 1325-1521

Astronomy of the AncientsAstronomy of the Ancients

Astronomy of the AncientsAstronomy of the Ancients

Aztec Sun Stone

Chinese Celestial Sphere, 400-600 CE

Careful observation over many decades provided the basis for agriculture, navigation, religion, and politics in many ancient cultures.

This rudimentary science was rooted in practical considerations with no real reason to pursue the “why” of it all.

The Golden Age: from The Golden Age: from ThalesThales to Ptolemyto Ptolemy

The path which led to what we now call science bega n in the Mediterranean, in ancient Greece, from about 500 BC E to 150 CE.

What is Science?

The collection of facts?The accumulation of detailed observations of the world?The attempt to understand how things work?The ability to predict the consequences of any action? The power to master nature?

The collection of facts?The accumulation of detailed observations of the world?The attempt to understand how things work?The ability to predict the consequences of any action?The power to master nature?

“I am an extraterrestrien. My work is to change humans genetically, so that they don’t murder earth. For this aim I’m using a time machine (Jesus is a clone of mine). I can proof everything I say.”…

“All stars have planets. Since billions of years developed Galaxy is a constitutional state. Killing planets is against the law. So Galaxy is obliged to interfere. As ambassador of United Planets of Galaxy I demand diplomatic immunity.”…

“Newton calculated the orbits of a planet around a star. But if masses are equal, Newton said the orbits are ellipses, but he made a mistake. The orbits are spirals. Even easier to show is that stars with helium are hotter (elastic impacts). It is easy to show that all stars have planets and calculate their orbits.” …

The joys of being a scientist

Or

The reason for learning more science

The Sanctity of the HeavensThe Sanctity of the Heavens

Plato [428-348 BCE]

“All heavenly motion must be in perfect circles moving at uniform speed. All heavenly objects must reside on perfect spheres.”

Aristotle [384-322 BCE]

“The Earth lies, unmoving, at the center of an eternal and unchanging Universe.”

MATCH THE NAME TO THE FACE

Aristotle

Plato

Nia Vardalos

Socrates

Aristarchus

The DissenterThe Dissenter

Aristarchus [310-230 BCE]

In about 260 BCE Aristarchus suggested a model of th e Universe in which the Earth moved around the Sun.

- perhaps to explain retrograde motion- he believed the Sun to be much bigger than the moo n- followed upon some work by Herakleides [ 388-315 BC E]

The price of perfectionThe price of perfection

The Geocentric Universe of the Greeks culminated in the quantitative model of Ptolemy [100-170 CE] which survived for about 1500 years.

Epicycles upon epicycles were to hinder progress in astronomy until 1606!

The book that nobody readThe book that nobody readDe Revolutionibus orbium coelestium - Canon Nicolas Copernicus (1543)

- only 4 reprints in 400 years! [ 1566, 1617, 1854, 1873]

Copernicus’ Heliocentric Universe

Epicycle count:

Ptolemy 40 Copernicus 48

The Watershed of ScienceThe Watershed of Science

Johannes Kepler [1571-1630]

Johannes Kepler was conceived on 16 May 1571 at 4.37am and was born on 27 December at 2:30pm, after a pregnancy lasting 224 days 9 hours and 53 minutes.

- recorded in a horoscope cast by Kepler himself

See Sleepwalkers by Arthur Koestler

“The accused appeared in court, accompanied, alas, by her son Johannes Kepler, mathematician.”

Court scribe at witchcraft trial of Katherine Kepler, 1615

“Mars is a star who defies observation”- Kepler in dedication of Astronomia Nova, 1609

“… those eight minutes point the road to a complete reformation of astronomy…”

- Ch. 19 Astronomia Nova, on the power of Tycho’s observations of Mars

“[Astronomers are] the priests of God, called to interpret the Book of Nature.”

- in Tertius Interveniens

The Harmony of the SpheresThe Harmony of the Spheres

The five Platonic solids

Mysterium Cosmographicum - Kepler, 1596

The figure that started it all.

Five perfect solids, five intervals between the six known planets.