ASTRONOMY

LIST OF ATRONOMERS

• Aristotle
• Aristarchus
• Ptolemy
• Copernicus
• Kepler

LIST OF ASTRONOMERS

• Galileo Galilei
• Newton
• Hubble

ARISTOTLE (384-322 BCE)

• Aristotle believed that Earth was the center of all things
• He thought that if Earth went around the sun, then the relative positions of the stars would change as Earth moves
• One of his most important contributions was defining and classifying the various branches of knowledge
• He contributed ethics as an important subject of philosophy

ARISTARCHUS (ABOUT 310-230 BCE)

• His biggest contribution was having proposed a heliocentric model of the solar system
• Aristarchus supported that the sun should be in the center of the universe, not the Earth
• He believed that the stars were very far away instead of lying just outside the orbit of Saturn
• He also attempted to measure the relative distance to the moon and sun
• This ratio of distance was much too small but was important in the use of observation and geometry to solve a scientific problem

PTOLEMY( ABOUT 100-170 CE)

• Ptolemy believed that a celestial body traveled at a constant speed in a perfect circle
• He developed a geocentric model that was used by astronomers for the next 14 centuries
• In his model, the planets moved on small circles that in turn moved on larger circles
• It's called the "wheels-on- wheels"
• It fit observations better than any model that had come before, it allowed prediction of the motion of planets years into the future

COPERNICUS (1473 - 1543)

• He felt that ptolemy's model of the solar system was too complicated
• Since time had changed little since the time of Ptolemy, Copernicus adopted his idea that planters paths should be perfect circles
• He used a "wheels-on wheels" system, but Copernicus's model fit observations a little better than ptolemy's geocentric model
• The heliocentric model of Copernicus is generally seen as the first step in the development of modern models of the solar system

KEPLER (1571 - 1630)

• He analyzed observations of the planets
• When he realized that requiring planetary motions to be exactly circular did not fit the observations perfectly, Kepler then tried other types of paths and found that ellipses fit best
• Kelleys big contribution was formulating three principles, which are now know as Kepler's laws

GALILEO GALILEI (1564 - 1642)

• He made a significant improvements to the newly invented telescope, and used his to view celestial objects
• Galileo observed the moons Io, Europe, Callsito, and Ganymede orbiting Jupiter and they are known as the Galilean satellites
• His observations showed that earth was not the on,y object that could not be orbited
• This gave support to the heliocentric model
• And last, he also observed that Venus went through places similar to the phases of earths moon, these phases result from changes in the direction that sunlight strikes Venus as Venus orbits the sun