Historical Models of our Solar Systemand

Kepler’s Laws of Planetary Motion

Geocentric Model

• Earth is center of our Solar System

• Aristotle- Over 2000 years ago,

• Unexplained on how planets appear to move backwards

• Ptolemy- Planets move in small circles or epicycles

Heliocentric Model

• Sun is center of our Solar System

• Copernicus- Over 450 years ago (1543 ad)

• First to suggest heliocentric theory and vaguely mapped out the planets orbiting the sun in a circular orbit.

Galileo

• Supporter of Copernicus’s Heliocentric theory

• House arrest • Observed moons

orbiting Jupiter and theorized objects can revolve around other planets not just Earth

Solar System precisely measured

• Tycho Brahe- studied Solar System and made very accurate recordings of his observations

• Tycho’s assistant, Kepler, used information for the details of orbits

Kepler’s Laws of Planetary Motion1st Law - Law of Ellipses

Each planet orbits the sun in a path called an ellipse or elongated circle

Ellipse is a closed curve whose path is determined by 2 points or foci within the ellipse

Focus 1 is the Sun and Focus 2 is an imaginary pointSemi-major axis = average distance from sun (AU); ½ major axis

Eccentricity

• Degree of elongation or shape of planet’s orbit

• Ratio between the foci and length of major axis

• Circular =0• Very elongated =1

2nd Law – Law of Equal Areas

• An imaginary line between the Sun and a planet sweeps out equal areas in equal times as the planet travels around the ellipse.

3rd Law – Law of Periods

• Mathematical relationship P2 = a3

• a= semi-major axis (planets average distance from Sun measured in AU’s)

• p= planet’s orbital period (time)

Newton

• Used Kepler’s Laws of planetary motion and published Principia for short. In this publication, considered to be the greatest piece of scientific literature ever written.

• Contains Newton’s laws of motion including universal gravitation.

Einstein (1879-1955)

• Changed Newton’s gravitational theory based on findings of Mercury’s orbit.

• Developed Theory of Relativity. It completely changed the way we study gravity and even changed our understanding of the universe.

Kepler’s Laws Simulations• Click http://www.physics.sjsu.edu/tomley/kepler.html

Bibliography• http://www.astro.umass.edu/~myun/teaching/a100/images/geocentric.jpg• http://www.physics.hku.hk/~nature/CD/regular_e/lectures/images/chap04/heliocentric.jpg• http://www.3villagecsd.k12.ny.us/wmhs/Departments/Math/OBrien/galileo5.jpg• http://galileo.rice.edu/sci/brahe.html• http://www.asu.cas.cz/~had/tycho.jpg• http://cseligman.com/text/history/ellipse2.jpg• http://www.windows.ucar.edu/the_universe/uts/kepler3_small.gif• http://library.thinkquest.org/27585/frameset_intro.html• http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/imgrel/merc.gif• http://zebu.uoregon.edu/~soper/Orbits/eccentricity.gif• http://www.physics.hku.hk/~nature/CD/regular_e/lectures/images/chap04/geocentric.jpg• http://outreach.atnf.csiro.au/education/senior/cosmicengine/images/cosmoimg/keplerellipse.gif