1. Astronomy in the Middle Ages to the Modern Era
From Copernicus to Galileo to man on the moon

2. Copernicus Began the process of disproving the geocentric theory
A heliocentric model of the universe offers a much simpler explanation of the universe (remember Occam’s Razor)

3. Heliocentric Model Explains retrograde motion
Planets will appear to change direction every time Earth overtakes their orbit
Could now determine the distance a planet is from the sun using geometry
There were still problems with his model because he said the orbits of the planets were circular
His views were slow to be accepted

5. Tycho and Kepler Copernicus opened the door to new ideas
A cultural renaissance was taking place in Europe
The Protestant Reformation had begun
The new world was being settled
It was an environment ripe for intellectual stimulation

6. Tycho Brahe
Believed that God placed the planets in the heavens as a sign to humankind of events on Earth
Made precise measurements with instruments he constructed

7. Tycho Brahe
First to show the existence of heavenly bodies outside of our solar system
Suggested that the heavens were more complex than we first believed
He had Earth still as the center of the universe with the Sun orbiting around it and the other planets orbiting the Sun

8. Johannes Kepler
Explained Brahe’s precise observations in mathematical terms
Developed three laws that explained most aspects of planetary motion

9. Kepler’s Laws
Law of Ellipses
Law of Equal Areas
Law of Periods

10. Law of Ellipses Each planet orbits the sun in an elliptical path
Each ellipse has two foci – one of which is the sun
This means the planet is not always the same distance from the sun
Have students draw an ellipse
If you draw a line from any point on the ellipse to teach of the two foci the total length of these lines will always be the same.

11. Law of Ellipses
Perihelion – the point where the planet’s orbit is closest to the sun
Aphelion – the point where the planet’s orbit is furthest from the sun
The distance given is usually the average of the perihelion and the aphelion

12. Law of Equal Areas
Describes the speed at which planets travel at different points in their orbits
Earth’s orbit is nearly a perfect circle with the sun off center
Earth moved faster when it was closer to the sun

13. Line from center for the sun to the center of the planet sweeps through equal areas in equal periods of time.
Both shaded areas have the same area. Shorter area moving faster, longer area moving slower.

14. Law of Periods
Describes the relationship between the average distance of a planet from the sun and the orbital period of the planet
Orbital period – the time it takes to make one revolution around the sun
The cube of the average distance of a planet from the sun (a) is always proportional to the square of the period (p)

15. The Mathematics K X a3 = p2 K is a mathematic constant
If we measure distance in AU and use earth-years, K = 1 and therefore a3 = p2
a = distance in astronomical units (AU)
p = orbital period
Examples: Earth is 1 AU and its period is 1 so 1 x 1 cubed = 1 squared and 1 = 1
Any errors are accounted for by the rounding off of distances or periods
Jupiter 5.2 AU’s and period is years – do the calculations

16. Kepler’s Three Laws
Describe the essential features of planetary motion around our Sun
Were the first laws to describe the heavens correctly
Kepler also gave us the word satellite

17. Galileo Galilei
Used the newly invented telescope to study the motions of the planets (Note: Galileo did not invent the telescope)
Proved that the heliocentric model was the correct one

18. Galileo Galilei
Was the first to use the telescope to study the heavens
Observed that the moon was a ball of rock
Observed sunspots and that they changed from day to day and deduced that the sun rotated
Discovered that Jupiter had moons
Examined the Milky Way and saw that it was made up of millions of stars
Observed that Venus went through phases just like the Moon

19. Galileo Galilei
That fact that Venus had phases left no doubt that it orbited the Sun and put an end to the Geocentric model of the universe
The originator of the scientific method still in use today
Was brought up on charges of heresy against the church (1992 the church admitted it made a mistake)

20. Newton’s Application of Kepler’s Laws
Newton wanted to know why the planets moved liked this
Newton said that a moving body will only change its motion if an outside force causes it to do so
An outside force must cause it to curve
This force he determined was gravity
The gravitational pull of the sun is what keeps the planets in orbit around it.
Inertia – straight line or at rest

21. Isaac Newton and the Birth of Astrophysics
Some consider him to be the greatest scientist of all time
Studying the moon he came up with the laws of gravity
Invented Calculus
His laws of gravity and motion were totally accepted for 200 years

22. The Growth of Astrophysics
New Planets were discovered
Stars had companions that orbit with them
Irregularities in the orbit of Uranus led to the discovery of Neptune
Bigger telescopes – Telescopes in space
Applying photography
Space Exploration