SOLAR SYSTEM TIMELINE

CURRENT

• Heliocentric or sun centered
• Earth and other planets orbit the sun
• Earliest models thought the earth was in the model
• Called: Earth-centered or geocentric

ARISTOTLE

• His model placed the moon, sun, planets, and stars on a series of circles that surrounded Earth
• He thought if the Sun went around the earth then the relative positions of the stars would change as Earth moves
• This apparently shift the position of an object when viewed from different locations known as a parallax
• The stars are so far away that parallax cannot be seen with the naked eye

ARISTARCHUS

• He is reported to have proposed a heliocentric model of the solar system
• Aristotle attempted to measure the relative distances to the moon and the sun- this was a major contribution to science
• His ratio of distances were much to small but was importantf in the use of observation and geometry to solve a scientific problem

PTOLEMY

• He wrote the book "Almagest"
• Base on observations that go back as far as 800 years ago
• He believed that a celestial body traveled at constant speed in a perfect circle
• "Wheels on wheels" system fit observerations better than model that had come before
• It allowed predictions of the motion of planets years into the future

COPERNICUS

• He felt that Ptolemy's model was to complicated In his time data was still based on observation with the naked eye He adopted Ptolemy's idea that planetary paths should be perfect circles Like Ptolemy he used a "wheels-on-wheels" system The heliocentric model of Copernicus is generally seen as the first step in the development of modern models of the solar system

KEPLER

• He then tried other types of paths and found that ellipses fit best Kelper formulated 3 principals which today are known as Kelper's laws 1st law states that planetary orbits are ellipses with the sun at one focus 2nd law states that planets move faster in their orbits when closer to the sun 3rd law relates the distance of a planet from the sun to the time it takes to go once around its orbit

GALILEO

• He made scientific improvements to the newly invented telescope He observed the moons Io, Europa, Callisto, & Ganymede orbiting Jupiter- today these moons are known as the Galilean Satellites His observations showed that Earth was not the only object that could be orbited-this gave support to the heliocentric model He also observed that Venus went through phases like the Earth- because where the sun hits Venus

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