Physcie Modern Astronomy

Early Views of the Universe

• Students should understand competing models of the universe: Geocentric (Earth-centered) and Heliocentric (Sun-centered). The models were developed by philosophers like Eudoxus, Aristotle, Ptolemy, Brahe, Aristarchus, Copernicus, Galileo, and Kepler.

Geocentric Model Overview

1. Eudoxus: Proposed concentric spheres for celestial bodies.

2. Aristotle: Believed in Earth as the universe's center.

3. Ptolemy: Elaborated a geocentric system of planets.

4. Tycho Brahe: Suggested Earth-centric solar system with planets orbiting the Sun.

Heliocentric Model Overview

1. Aristarchus: Suggested a sun-centered universe.

2. Nicolaus Copernicus: Asserted the inert sun at the center.

3. Galileo Galilei: Used a telescope, observed celestial phenomena that challenged existing views (sunspots, moon's surface, Jupiter’s moons).

4. Johannes Kepler: Discovered that planets move in elliptical orbits and proposed the Law of Ellipses, where the Sun is located at one focus of the ellipse.

Law of Elipses

1. Each planet's orbit about the Sun is an ellipse.

2. The Sun's center is always located at one focus of the orbital ellipse. The Sun is at one focus.

3. The planet follows the ellipse in its orbit, meaning that the planet to Sun distance is constantly changing as the planet goes around its orbit.