Gravitation

Page
1

Slide 1

Early Astronomy

As far as we know, humans have always been interested in the motions of objects in the sky.

Not only did early humans navigate by means of the sky, but the motions of objects in the sky predicted the changing of the seasons, etc.

Slide 2

Early Astronomy

There were many early attempts both to describe and explain the motions of stars and planets in the sky.

All were unsatisfactory, for one reason or another.

Slide 3

The Earth-Centered Universe

A geocentric (Earth-centered) solar system is often credited to Ptolemy, an Alexandrian Greek, although the idea is very old.

Image from: http://abyss.uoregon.edu/~js/ast123/lectures/lec02.html

Slide 4

Ptolemy’s Solar System

Ptolemy’s solar system could be made to fit the observational data pretty well, but only by becoming very complicated.

Image from: http://abyss.uoregon.edu/~js/ast123/lectures/lec02.html

Slide 5

Copernicus’ Solar System

The Polish cleric Copernicus proposed a heliocentric (Sun centered) solar system in the 1500’s.

Image from: http://abyss.uoregon.edu/~js/ast123/lectures/lec02.html

Slide 6

Objections to Copernicus

How could Earth be moving at enormous speeds when we don’t feel it?

(Copernicus didn’t know about inertia.)

Why can’t we detect Earth’s motion against the background stars (stellar parallax)?

Copernicus’ model did not fit the observational data very well.

Slide 7

Galileo & Copernicus

Galileo became convinced that Copernicus was correct by observations of the Sun, Venus, and the moons of Jupiter using the newly-invented telescope.

Perhaps Galileo was motivated to understand inertia by his desire to understand and defend Copernicus’ ideas.

Slide 8

Tycho and Kepler

In the late 1500’s, a Danish nobleman named Tycho Brahe set out to make the most accurate measurements of planetary motions to date, in order to validate his own ideas of planetary motion.

Slide 9

Tycho and Kepler

Tycho’s data was successfully interpreted by the German mathematician and scientist Johannes Kepler in the early 1600’s.