Astronomers in history

Aristotle

• Aristotle thought Earth was the center of all things
• His model placed the moon, sun, planets and stars circling Earth
• Aristotle founded the shift in position of an object when viewed from
• different locations is known as Parallax.

ARISTARCHUS

• Aristarchus was reported to have proposed a heliocentric model of the solar system
• He tried to measure the relative distance to the moon and sun
• Aristarchus's ratio was much to small but was a important in the use of observation
• and geometry to solve a scientific problem

Ptolemy

• Ptolemy created a geocentric model that astronomers would use for the next 14 centuries
• He believed that a celestial body traveled at a constant speed in a perfect circle
• He created the "wheels on wheels" system that fit observations better than anything before

Copernicus

• He believed that planetary paths should be perfect circles
• He also used the Wheels on Wheels system
• His model fit observations a little better than Ptolemy

Kepler

• Kepler realized that requiring planetary motion not to be perfectly circular
• He then tried other types of paths and found eclipses fit best
• Kepler formulated Three Laws called Kepler's Laws

Galileo

• Galileo made very significant improvements to the telescope
• He used this new telescope to view celestial objects
• Galileo observed the moons Io, Europa, Callisto and Ganymede