1. Early Astronomers and their Ideas

2. Ptolemy Claudius
In A.D. 140, Greek astronomer wrote a book that combined all the ancient theories about the astronomy.
He expanded Aristotle’s theories with careful mathematical calculations in his “Ptolemaic Theory”. According to his Theory the Earth was at the center of the universe. Sun and other planets revolved around the Earth.
He predicted the motion of planets that was better than any other astronomer.

3. Nicolaus Copernicus
In 1543 Nicolaus Copernicus published a new theory. According to his theory the Sun is at the center of the universe, and all planets revolve around the Sun.
This theory was not accepted at that time,

4. Tycho Brahe
Danish Astronomer Tycho Brahe used several tools to observe the sky.
Tycho favored earth-centered theory which was different from Ptolemy.
He believed that sun and moon revolved the Earth, but other planets did not. The other planets revolve around the Sun.
His theory was not correct, but he kept precise and correct observations for years.

5. Johannes Kepler
Tycho had an assistant who continued his work after his death.
Kepler did not agree with Tycho’s theory.
He realized that the data Tycho collected was accurate and valuable.
Kepler announced the new laws of planetary motion based on the data.
Kepler stated that the planets revolve arround the Sun in eliptical orbits.
The Sun is not in the exact center of the orbits.

6. Galileo Galilei
Galileo became the first person to use a telescope to observe celestial bodies.
His telescope was very simple.
He discovered the following
Four moons orbiting Jupiter
Craters and mountains on the moon
Sunspots on the sun
Phases of Venus
His discoveries proved that the planets are not dots of lights. They are physical bodies like the Earth.
Galileo favored the theory of Copernicus.

7. Isaac Newton Newton explained why planets revolved around the sun.
He explained that the gravity is the force that holds the planets in orbit around the sun.
Newton’s Laws of Motion and Gravity provided for the basis of modern theory.

8. Tools of Early Astronomer’s
Replica of Newton’s Telescope

9. Galileo’s Telescope
Galileo’s telescope

10. Tycho’s Instruments

11. Kepler’s Laws

12. Reflecting Telescopes

13. Radio Telescope

14. Hubble Telescope

15. Schmidt Telescope