1. Observing the Solar System: A Historical Perspective

2. Geocentric Model
The Church heavily influenced the Greek and Roman philosophers and their view on science.
The belief in the geocentric universe- Everything was Earth centered especially the solar system.

3. The movement of the stars explained by a sphere around us that rotated.
Interest in movement of stars led to development of calendar.
Noticed retrograde motion but geocentric model could not explain.

4. Heliocentric Model
Polish astronomer Nicolas Copernicus ( ) questioned the church and the geocentric model but did not speak out for fear of persecution.
Heliocentric model explained retrograde motion.
His work was published after he died but only in Latin so the general public could not read it. Even academics were not willing to confront the Church.

5. Galileo Galileo is often considered the founder of modern astronomy.
He perfected the refraction telescope in 1609.
With it he could see the 4 Jovian moons. He drew diagrams of valleys, mountains and craters of the moon and observed sunspots.
He published these observations in a book called Starry Messenger in 1610 and laid the foundations for years of trouble with the Catholic Church!

6. The Church regarded the circular objects of the sun and moon as perfect. Galileo’s observations suggested that they were not!
Galileo viewed Jupiter and its moons to be a smaller version of our solar system and became convinced of the Heliocentric Model.
The Church ordered him to retract his claims and he refused!

7. In 1632 he published a book in Italian presenting this forbidden view of the Sun at the center of the solar system.
The Church placed him under arrest until his death 4 years later.

8. Not until 1992 did the Catholic Church officially remove Galileo from any wrongdoings!
In his honour, the Galileo spacecraft was launched in 1989 by NASA to explore Jupiter and its moons.

9. Tycho Brahe 16th Century Danish nobleman
Observational astronomer without the aid of a telescope.
Particularly interested in orbit of Mars.
Had difficulty believing the Earth was moving (Heliocentric) because it could not be felt.
Tycho died before his Mars data could be used.

10. Johannes Kepler Kepler was an assistant of Brahe
Was a mathematician not an observer which helped to solidify the Heliocentric movement.
Developed 3 laws from the hundreds of pages of data.
Law of Ellipses, Law of Equal Areas and the Law of Harmonies.

11. #1. Orbit is elliptical with Sun at one focus
#1. Orbit is elliptical with Sun at one focus. Distance from the Sun changes throughout orbit.
#2. Area traveled is equal but speed is not constant. Travel faster closer to the sun.
#3. The period of a planet squared is equal to its cubed mean distance from the Sun.

12. Isaac Newton
Kepler new that there must be a force required to keep the planets in motion around the Sun.
Newton’s laws introduced the force of gravity to the explanation.
His laws explained orbits, motion of comets around our Sun, elliptical orbits…
Most of the phenomenon we see in space is explained with Newton’s Laws.