### Geocentric Model

A representation of the universe in which starts and planets revolve around Earth

Ptolemy proposed the model

### Tycho Brahe

Last astronomer without a telescope

Provided Kepler with the data needed in order to develop his three Laws

### J. Kepler

Three Laws of Planetary Motion

With the universal law of gravity and Newtons laws (especially the 2nd), you can can get all Keplers laws

### Kepler's 1st Law

Law of Ellipses:

The orbit of a planet is an ellipse where one focus of the ellipse is the sun

### Kepler's 2nd Law

Law of Equal Areas:

A line from the planet to the sun sweeps out equal areas in equal amounts of time

### Kepler's 3rd Law

Law of Harmonies:

The period of a planet's orbit squared is proportional to its average distance from the sun cubed

P^ = a^

### Galileo

1st astronomer to use a telescope

Used a telescope and challenged the conventional wisdom of the motion of objects and the nature of the heavens

### Galileo's Observations

(a and b below challenged the geocentric model, c and d challenged the idea that the heavenly object were perfect)

Telescope observations:

a) Phases of Venus

b) Moons of Jupiter

c) Sunspots

d) Mountains on the Moon

### Newton's 1st Law of Motion

Law of Inertia:

A body remains at rest, or moves in a straight line (at a constant velocity), unless acted upon by a net outside force

### Newton's 2nd Law of Motion

F = ma:

The acceleration of an object is proportional to the force acting upon it