Chapter 2 The Copernican Revolution

Chapter 2 The Copernican Revolution

Units of Chapter 2 2.1 Ancient Astronomy 2.2 The Geocentric Universe 2.3 The Heliocentric Model of the Solar System The Foundations of the Copernican Revolution 2.4 The Birth of Modern Astronomy

Units of Chapter 2, continued 2.5 The Laws of Planetary Motion Some Properties of Planetary Orbits 2.6 The Dimensions of the Solar System 2.7 Newton s Laws The Moon is Falling! 2.8 Newtonian Mechanics Weighing the Sun

2.1 Ancient Astronomy Ancient civilizations observed the skies Many built structures to mark astronomical events Summer solstice sunrise at Stonehenge:

2.1 Ancient Astronomy Spokes of the Big Horn Medicine Wheel are aligned with rising and setting of Sun and other stars

This temple at Caracol, in Mexico, has many windows that are aligned with astronomical events 2.1 Ancient Astronomy

2.2 The Geocentric Universe Ancient astronomers observed: Sun Moon Stars Five planets: Mercury, Venus, Mars, Jupiter, Saturn

2.2 The Geocentric Universe Sun, Moon, and stars all have simple movements in the sky Planets: Move with respect to fixed stars Change in brightness Change speed Undergo retrograde motion

2.2 The Geocentric Universe Inferior planets: Mercury, Venus Superior planets: Mars, Jupiter, Saturn Now know: Inferior planets have orbits closer to Sun than Earth s Superior planets orbits are farther away

2.2 The Geocentric Universe Early observations: Inferior planets never too far from Sun Superior planets not tied to Sun; exhibit retrograde motion Superior planets brightest at opposition Inferior planets brightest near inferior conjunction

2.2 The Geocentric Universe Earliest models had Earth at center of solar system Needed lots of complications to accurately track planetary motions

The Geocentric Theory The earth is located at the center of the universe and all the planets revolve around the earth.

The Geocentric Theory The Geocentric theory was believed by the Catholic church especially because the church taught that God put earth as the center of the universe which made earth special and powerful. The idea of the Earth actually moving was widely felt as a foolish suggestion because, as they saw it, if the Earth was moving they would be able to feel it.

Aristotle (384-322 B.C.) Developed an early model based on the concept of uniform circular motion. He placed the earth at the center of the universe and all of the planets, sun and stars around it. When Aristotle lived, if a person could reason out why something happened, then you didn t need to do any experiments to see what would happen.

In the realm of change, the natural motion of earthy materials was to seek the center of the universe. This is why Aristotle placed the earth at the center of the cosmos. This is also his explanation for why objects fall when dropped. A dropped object is just following its natural tendency to seek the center of the universe.

Aristotle reasoned that if the earth rotated about its axis, we should fly off into space. Since we don't, the earth must be stationary. It would be almost 1900 years before Galileo introduced the concepts of gravity and inertia that explain why these effects are not observed even though the earth does move.

Greek Contributions The Ancient Greek philosophers refined astronomy, changing it from merely observational science into a full-blown theoretical science.

Greek Contributions The ancient astronomers used astronomy to track time and cycles, for agricultural purposes, as well as adding astrology to their sophisticated observations. Rather than generating astronomical theories, they were more concerned with what was happening and when, but without addressing the why, other than vague attributions to Gods and astrology.

Ptolemy (140 A.D.) Ptolemy advanced the geocentric theory in a form that prevailed for 1400 years. He added mathematics to support the theory

Ptolemy s Problem Many supporters of the geocentric theory had one piece of evidence they couldn t explain the movement of MARS. Let s take a break and investigate this movement.

Mars Motion http://csep10.phys.utk.edu/astr161/lect/retrograde/retrograde.html

How did Ptolemy Explain this Problem? Ptolemy used geometric models to predict the positions of the sun, moon, and planets, using combinations of circular motion known as epicycles. An epicycle is an orbit within an orbit Having set up this model, Ptolemy then went on to describe the mathematics which he needed in the rest of the work.

Ptolemy s Model Epicycles Included