Early Astronomers and their Ideas

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.

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,

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.

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.

Galileo Galilei

• Galileo became the first person to use a telescope to observe celestial bodies.

• His telescope was very simple.• He discovered the following1. Four moons orbiting Jupiter2. Craters and mountains on the moon3. Sunspots on the sun4. Phases of VenusHis discoveries proved that the planets are not dots of lights. They are physical bodies like the Earth.Galileo favored the theory of Copernicus.

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.

Tools of Early Astronomer’s

Replica of Newton’s Telescope

Galileo’s Telescope

Galileo’s telescope

Tycho’s Instruments

Kepler’s Laws

Reflecting Telescopes

Radio Telescope

Hubble Telescope

Schmidt Telescope