7.4 The Solar System(Pages 291-296)

Learning Goals

• I can differentiate between the geocentric and heliocentric models of the solar system.

• I can describe retrograde motion and explain why it happens.

• I can describe the properties of the inner planet and the outer planets.

Models of the Solar System

• Geocentric model (geo means Earth) àEarth is the centre of all planetary motion, with the planets and the Sun travelling it in perfect circles

• Heliocentric model (helio means Sun) àSun is at the centre of the solar system and has the planets orbiting around it in perfect circles

Thecurrentheliocentric (Sun-centered)modelofthesolarsystemwasfirstintroducedinthe1500sbyPolishastronomerNicolausCopernicus.

Previousmodelsofthesolarsystemweregeocentric(Earth-centered),originatingwiththeGreekastronomerPtolemy.

The Planets

• Planet: an object that orbits one or more stars (and is not a star itself), is spherical, and does not share its orbit with another object

• Solar system: a group of planets that circle one or more stars

The Planets

Image above shows relative size correctly, but not relative distance.

Retrograde Motion

• Retrograde motion: the movement of an object in the sky, usually a planet, from east to west, rather than in its normal motion from west to east

• Produced when Earth catches up with and passes an outer planet in its orbit

Retrograde Motion

Trythisflashanimationtolearnaboutretrogrademotion(bestviewedinFirefox):http://www.mytextbook.ca/product/9780070318618/itr/ppt/assets/OS9.PPT.U3.CH7.slide35.Retro_Nav.swf.html

Distances between the Planets

• Astronomicalunit(AU):theaveragedistancebetweenEarthandtheSun– About150× 106 km

• Orbitalradius:theaveragedistancebetweentheSunandanobjectthatisorbitingtheSun

Classifications of the Planets• Inner planets

– Mercury, Venus, Earth, Mars– Called the terrestrial (Earth-like) planets– Relatively small, have solid cores and rocky crusts

• Outer planets– Jupiter, Saturn, Uranus, Neptune– Formed from large clumps of gas, ice, and dust– Large gaseous bands and cold temperatures– Called gas giants

Want to see the distance between planets?

http://lasp.colorado.edu/education/outerplanets/orbit_simulator/

Properties of the Planets

Practice

• Page 296 # 1-8