Developing the Science of Astronomy (Power Point 03)

Student Learning Objectives Examine the contributions of ancient and modern astronomy to the understanding of gravity and planetary motion. Identify contributions from the first Astronomers and compare the models Recall the contributions of Galileo and analyze the significance of these contributions

How did early Greek philosophers describe motions in the sky? The Greeks had 3 basic theories for the sky All heavenly bodies are spheres that move in circles Heavens are unchangeable Earth is stationary at center of universe Most Greeks in B.C. times believed in the geocentric model.

Aristotle (300 BC) Eratosthenes (200BC) Placed Earth at the center of the universe by logic (persisted for 2000 years) Eratosthenes (200BC) Measured circumference of Earth using observation and simple geometry Image Credit: sciencebuddies.org

Practice Explain why Aristotle would have assumed Earth is at the center of the system. How does this support the Celestial Sphere Model? Why is this model still useful to us today?

Hipparchus & Magnitudes Hipparchus (150 BC) Divided the stars into apparent magnitudes by comparing them according to their brightness Magnitudes are a measure of brightness. Sun −26.7 Full Moon −12.6 Venus −4.4 Vega Naked Eye Limit +6 Binoculars Limit +10

Practice 1) Which would appear fainter to us when viewed from Earth with our eyes?   −4 magnitude star +4 magnitude star 0 magnitude star 2) If two stars have the same energy output, what would make one star appear fainter than the other, when viewed from Earth?

The Epicylce Model Ptolemy (150 AD) Developed the epicycle model to explain Mars “backwards”, or retrograde motion Today’s Astrology is based on principles developed by Ptolemy (fun fact) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

Ptolemy’s Epicycle Model https://www.youtube.com/watch?v=EpSy0Lkm3zM

Copernicus (mid-1500’s) Heliocentric Model Used mathematics to determine the Sun was at the center of the solar system Heliocentric Model Image Credit: slideshare.net

The Early Models Aristotle Ptolemy Copernicus Stationary Earth Rotating Earth Earth at Center Sun at Center Circular Motion Circular motion Orbital speeds same for all depend on distance Based on Observation of Apparent Motion Mathematics Practice Write a compare and contrast sentence which relates these models.

The Transition to Modern Science Galileo (1600’s) Used observations - Venus goes through phases like the Moon - to provide visual proof of Copernicus’s Sun centered system First to use telescope to view sky

Galileo’s Telescope Observations Venus goes through phases as it orbits the Sun Planet positions confirmed Moon & Sun not perfect spheres Objects orbiting Jupiter (not Sun or Earth) Image Credit: commons.wikimedia.org

Image Credit: wordpress.com

Practice Analyze and describe the significance of the following discoveries made by Galileo in terms of confirming or refuting earlier models. Venus goes through phases like the Moon Visually confirmed relative locations of planets Observed objects orbiting Jupiter