Geocentric vs Heliocentric Theory Claims and Evidence from

“Geocentric vs. Heliocentric Theory” Claims and Evidence from the Ancient Astronomers Cornell Notes pg. 53

Astronomy • The study of celestial objects such as moons, planets, stars, and galaxies. • One of the oldest branches of science.

Moving Back in time… • Think back to over 2000 years ago. No high tech equipment for studying the far reaches of space… no idea of the law of gravity… scientists were stilling trying to develop basic explanations for the world.

Geocentric • CLAIM: Earth is the center of the universe Theory – Sun, planets, and stars all rotate around the earth. • EVIDENCE: things appear to move around Earth; Earth doesn’t feel like its moving…

Basic Assumptions about the Universe… • Everything outside of Earth is perfect – Planet shapes are perfect spheres – Orbits of Planets are perfect spheres – Stars are fixed to an outer sphere

Aristotle 384 • CLAIM: 5 elements each have a natural -322 BC place in the universe. Earth at center (geocentric). • EVIDENCE: earth sinks in water…gas bubbles rise, fire rises above air… etc. – Scientific teachings were taught for over 1000 years, but never tested!

A Problem • Retrograde Motionplanets temporarily with the appear to move Geocentric backwards Model…

Ptolemy 90 -168 AD • CLAIM: Celestial bodies revolve around the Earth (geocentric). • EVIDENCE: created a model of space that could be used to predict future positions of planets AND explained retrograde motion http: //www. polaris. iastate. edu/Eve ning. Star/Unit 2/unit 2_sub 1. htm

Heliocentric • CLAIM: The sun is at the center with planets Theory revolving around the sun. • EVIDENCE: failure of Ptolemy’s model over time; retrograde motion can be explained simply if earth is moving, too. http: //www. polaris. iastate. edu/Evenin g. Star/Unit 2/unit 2_sub 2. htm

Copernicus • Given credit as 1473 -1543 AD developing the Heliocentric Theory. • Created a simpler, more accurate model that could be used to predict future locations of planets. – Other Claims: earth is spinning on axis and revolving around the sun.

Brahe • CLAIM: Moon’s orbit 1546 -1601 AD isn’t a perfect circle, it’s an ellipse. • EVIDENCE: careful observations with diligent records. – (Brahe actually supported the Geocentric Theory)

Brahe’s model of our solar system to explain the phases of Venus

Kepler • CLAIM: Planets do not 1571 -1630 AD orbit in perfect circles but instead orbit in ellipses. • EVIDENCE: used records collected by Brahe • This discovery was the last piece needed to perfect Copernicus’s model. (Still not widely accepted).

Galileo • CLAIM: our moon has 1564 -1642 AD craters and the sun has spots (they’re not perfect!); and Jupiter has it’s own moonsthey don’t orbit the earth! • EVIDENCE: observations made through his carefully crafted telescope

Sir Isaac Newton 1642 -1727 AD • Defined the Laws of Motion and the Law of Gravity. • Now our solar system makes sense!