Ch 29 The Solar System

Over 2000 years ago: The Greek philosopher, Aristotle, proposed 55 concentric circles to which celestial objects were attached, and which rotated at different velocities.

Aristotle could not explain the retrograde motion...

FF 500 years

Geocentric Model

Ptolemy model - epicycles

Proposed model: each planet has 2 motions; revolution around the earth, & a series of small circles called epicycles

Epicycleshttp://csep10.phys.utk.edu/astr161/lect/retrograde/aristotle.html

Heliocentric Model

Copernicus (1473-1543)

Over 450 years ago

Sun-centered model

• All planets circle the sun, but at different speeds.

• Distances from the sun has direct relationship to the size of orbit.

He is credited for the start of the Scientific Revolution.

Galileo Galilei

• Made telescopes• Challenged Aristotle’s view of

motion• Supporter of Copernicus’s

Heliocentric theory• Convicted of heresy and placed

under house arrest • Observed moons orbiting Jupiter

and theorized objects can revolve around other planets not just Earth

• Discovered sunspots

1564 - 1642

Solar System precisely measured• Tycho Brahe- studied

Solar System and made very accurate recordings of his observations

• Tycho’s assistant, Johannes Kepler,

used information for the details of orbits

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

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

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

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

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 = r3

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

• p = planet’s orbital period (time)

Every planet has the same ratio!

Isaac Newton

• Used Kepler’s Laws of planetary motion and published Principia. Considered to be the greatest piece of scientific literature ever written.

• Contains Newton’s laws of motion including universal gravitation.– 1st law: An object will stay in its present

state of motion unless acted upon by a net force (Law of Inertia)

– 2nd law: F = ma– 3rd law: For every action there is an

equal and opposite reaction

Einstein (1879-1955)

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

• Developed Theory of Relativity.

Completely changed theway we study gravity andeven changed ourunderstanding 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