Lesson 2 Models of the Universe Geocentric Theory

Lesson 2 Models of the Universe

Geocentric Theory Ancient Greece

Geocentric Model • Earth Centered Universe • All objects move around Earth, a fixed point.

Problems with Geocentric Theory 1. This model does explain apparent motions of celestial (space) objects

Geocentric Model: Ptolemy (87 -150 AD) Used epicycles to explain planetary movements

Ptolemy’s system provided the first framework for all discussion of the universe for nearly 1500 years!! But… there was a problem…

Heliocentric Theory

Heliocentric Model • Sun Centered Universe • All celestial objects in the Solar system move around the Sun

Copernicus (1473 -1543) • Suggests a model that the Sun was the center of the universe. • Argued that the motion of the Sun & planets could be equally described by a Sun centered (heliocentric) system.

Tycho Brahe (1546 -1601): the greatest of the pre-telescope observers in Europe. 20+ years measuring the positions of the Sun, Moon and planets with great accuracy.

Copernicus (1473 - 1543) Johannes Kepler (1609) • Johannes Kepler was an assistant to Tycho Brahe. He used Brahe’s observations to study the orbit of Mars • Discovered three laws of planetary motion: predict with accuracy the motions of the planets

• Galileo (1564 -1642) first scientist to use a telescope to observe the sky. He observed the phases of Venus and the moons of Jupiter. Both observations supported the heliocentric model.

Kepler’s Laws

1 st Law Each planet’s orbit is an ellipse with the Sun at one focus.

Eccentricity A number indicating the roundness of an ellipse. Eccentricity = Distance Between Foci Length of Major Axis e=d/L

Perfect circle Straight line e=0 e=1

ESRT pg 15

Eccentricity Practice

2 nd Law Planets change orbital speed as they revolve around the Sun.

Caused by the Sun’s gravitational pull

3 rd Law • As distance from the Sun increases, a planet’s period of revolution increases.

ESRT pg 15