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STS-PPT

1. SCIENCE, TECHNOLOGY & SOCIETY HERMINIGILDA P. BALUBAR, EdD

2. Models of The Solar System What is a planetary system? A planetary system is a star and all of the celestial bodies that revolve around it. An example of a planetary system is the solar system which includes the sun and the planets and other celestial bodies orbiting the sun. Models of the Solar System ( C) Copyright 2014 - all rights reserved www.cpalms.org

3. What is the Center of the Solar System? The early scientists, in their attempt to answer this fundamental question created various models of the solar system. Models, which placed Earth at the center, are called Earth-centered, or geocentric , models. Models of the Solar System ( C) Copyright 2014 - all rights reserved www.cpalms.org http://childrenlearningonline.net/children-science-Lessuniver1.html

4. The Geocentric Model The early philosopher and astronomer believed that everything in the universe is “perfect”; and that the planets are perfect spheres circling in perfect circular orbits. They believed the Earth was the most important object in space and therefore assumed it to be the center of the universe. Models of the Solar System (C) Copyright 2014 - all rights reserved www.cpalms.org http://commons.wikimedia.org/wiki/File:Ptolemaic_system_2_(PSF).png

5. The Geocentric Model Aristotle, a Greek philosopher reasoned that if Earth circled around the sun, then the relative positions of the stars would change as Earth moves. This apparent change in the position of an object when viewed from different angles or locations on Earth is known as parallax . What Aristotle did not take into account is the fact that stars are very far away. At such great distance parallax cannot be observed without a telescope. Models of the Solar System (C) Copyright 2014 - all rights reserved www.cpalms.org

6. The Geocentric Model The geocentric model of the solar system became a very important part of ancient Greek Astronomy beginning in the sixth century B.C.E. The Greek philosopher Aristotle (384–322 B.C.E.) was among the first scholars to put forward an Earth-centered model of the Solar System. His model positioned the moon, sun, planets, and stars on a series of circles that moved around Earth. Models of the Solar System (C) Copyright 2014 - all rights reserved www.cpalms.org

7. The Geocentric Model Aristarchus, a Greek astronomer and mathematician, is believed to have proposed a sun-centered model of the solar system. Ptolemy an astronomer, geographer, and mathematician, exploited Aristotle’s Earth-centered view and developed a complex geocentric model that was used by astronomers over the next thousand years. Models of the Solar System (C) Copyright 2014 - all rights reserved www.cpalms.org

8. The Geocentric Model According to Ptolemy’s model, the planets moved on small circles that in turn moved on larger circles. Historical Models of the Solar System (C) Copyright 2014 - all rights reserved www.cpalms.org http://commons.wikimedia.org/wiki/File:Geocentric_system.png

9. The Geocentric Model Ptolemy’s “wheels-on-wheels” model seemed to make sense since it very well illustrated observations made at the time going back hundreds of years. Scientist for many centuries used Ptolemy’s model to make predictions of the motions of planets years into the future. Historical Models of the Solar System (C) Copyright 2014 - all rights reserved www.cpalms.org

10. The Heliocentric Model (Sun-Centered) Historical Models of the Solar System (C) Copyright 2014 - all rights reserved www.cpalms.org https:// www.flickr.com /photos/ nasablueshift /7368861386/

11. The Heliocentric Model The model which placed the sun at the center is called the heliocentric or sun-centered model. The Polish astronomer Nicolaus Copernicus watered-down Ptolemy’s model of the solar system since he thought the model was way too complicated. Although Copernicus adopted Ptolemy’s idea that planets’ orbits are perfect circles, he however developed Aristarchus’s primitive sun-centered model into a well thought out heliocentric model. Models of the Solar System (C) Copyright 2014 - all rights reserved www.cpalms.org

12. Epicycles to explain retrograde motion Earth Deferent Epicycle Planet Ptolemy also used minor epicycles, off-center circles, and other geometrical tricks to explain details of planetary motion.

13. The Copernican Revolution

14. Today: The Copernican model and how it explains motions of stars, sun, moon, planets Sizes and speeds of planetary orbits Reactions to Copernicanism

15. Nicolaus Copernicus (Mikolaj Koppernigk) 1473-1543

16. De Revolutionibus (“Revolutions”) (published 1543)

17. Aristotelian vs. Copernican

18. Motion of Stars and Sun (according to Copernicus)

19. Motion of Planets (according to Copernicus)

20. Sizes of Planetary Orbits 45º 45º Earth 1.0 A.U. 1 A.U. = “Astronomical Unit” = Earth-Sun distance Venus always appears within 45º of the sun.

21. Sizes of Planetary Orbits 45º 45º Earth Venus 1.0 A.U. 0.7 A.U. 1 A.U. = “Astronomical Unit” = Earth-Sun distance

22. Speeds of Planetary Orbits Earth Venus Venus crosses in front of the sun every 1.6 years. During this time, Venus must orbit 2.6 times. Set up a ratio to find time for one orbit: 1.6 years 2.6 orbits x years 1 orbit = x = 1.6/2.6 years = 0.62 years