Physics 202: Introduction to Astronomy – Lecture 3

Carsten Denker

Physics DepartmentCenter for Solar–Terrestrial

Research

January 25, 2006 Center for Solar-Terrestrial Research

Chapter 1.2 – 1.3 Planetary motion Retrograde motion Geocentric model Aristotle Epicycle Deferent Ptolemaic model Aristarchus of

Samos Heliocentric model

Copernican revolution

Modern Astronomy The Scientific Method

Theory Predictions Observations

Galilean moons Venus phases Sunspots

January 25, 2006 Center for Solar-Terrestrial Research

Ancient Greek Physical (geocentric) model

of the cosmos by Aristotle (384 – 322 BC)

Mathematical model of planetary motion by Ptolemy (100 – 170), terrestrial/celestial sphere, basic elements: earth, water air, and fire/quintessence

The Aristotelian cosmos. The Earth sits motionless at the center of the universe, and the outer sphere, the Primum Mobile, is assumed to undergo a full revolution in 24 hours.

January 25, 2006 Center for Solar-Terrestrial Research

Epicycle and Deferent

January 25, 2006 Center for Solar-Terrestrial Research

Mercury transit on 15 November 1999

January 25, 2006 Center for Solar-Terrestrial Research

Venus Transit 8 June 2004

January 25, 2006 Center for Solar-Terrestrial Research

The Phases of Venus Why did Plato

propose that all heavenly motion was uniform and circular?

How do the epicycles of Mercury and Venus differ from those of Mars, Jupiter, and Saturn?

January 25, 2006 Center for Solar-Terrestrial Research

Phases of Venus in 2004

January 25, 2006 Center for Solar-Terrestrial Research

Nicholas Copernicus (1473–1543)

De Revolutionibus Orbium Coelestum in 1543

Heliocentric planetary model: The Sun is at the center of all planetary motions, except for the Moon which orbits Earth. Under this arrangement the orbital speed of planets decreases steadily outwards, and the outer sphere of fixed stars is truly motionless. In Copernicus' original model the Earth has three motions: a daily 24-hr axial rotation, a yearly orbital motion about the Sun, and a third motion, somewhat related to precession which Copernicus thought necessary to properly reproduce ancient observations.

January 25, 2006 Center for Solar-Terrestrial Research

Galileo Galilei (1564 – 1642)First telescopic observations of the Sun!

January 25, 2006 Center for Solar-Terrestrial Research

Retrograde Motion of Planets

January 25, 2006 Center for Solar-Terrestrial Research

Retrograde Motion of Mars in 2003

January 25, 2006 Center for Solar-Terrestrial Research