The Solar SystemThe Solar System

ExplorersExplorers

Ancient GreeksAncient Greeks The ancient greeks noticed that the stars would The ancient greeks noticed that the stars would

move across the sky, but would stay in the move across the sky, but would stay in the same position relative to each other.same position relative to each other.

They came up with the word planet which They came up with the word planet which means “wandering star”.means “wandering star”.

Many greek scientists, such as Aristotle, Many greek scientists, such as Aristotle, believed that the universe is perfect and finite believed that the universe is perfect and finite and that and that Earth is stationary at its centerEarth is stationary at its center. .

Geocentric SystemGeocentric System ““geo”= greek word geo”= greek word

for Earthfor Earth

In a geocentric In a geocentric system, Earth is at system, Earth is at the center of the the center of the revolving planets. revolving planets.

Ptolemy (A.D. 140)Ptolemy (A.D. 140) Ptolemy was a greek astronomer who, like the earlier Ptolemy was a greek astronomer who, like the earlier

greeks, thought that the greeks, thought that the Earth was at the center of Earth was at the center of the universethe universe..

He agreed that the other planets rotated around Earth, He agreed that the other planets rotated around Earth, and explained that the planets move in little circles that and explained that the planets move in little circles that move in bigger circles. He thought this explained why move in bigger circles. He thought this explained why the planets seem to move at different speeds and even the planets seem to move at different speeds and even backwards.backwards.

People People believed Ptolemy's theorybelieved Ptolemy's theory for the next 1400 for the next 1400 years. years.

Copernicus (early 1500's)Copernicus (early 1500's) Copernicus was a polish Copernicus was a polish

astronomer who thought astronomer who thought that the that the sun was at the sun was at the centercenter of the system of of the system of planets. planets.

In a In a heliocentric systemheliocentric system, , Earth and the other planets Earth and the other planets (Mercury, Venus, Mars, (Mercury, Venus, Mars, Jupiter and Saturn) revolve Jupiter and Saturn) revolve around the sun.around the sun.

HeliosHelios is greek for is greek for “sun”.“sun”.

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How is Copernicus's description of the How is Copernicus's description of the system of planets different from system of planets different from Ptolemy's description?Ptolemy's description?

GalileoGalileo An Italian astronomer who supported Copernicus's An Italian astronomer who supported Copernicus's

heliocentric explanation and disproved Ptolemy's heliocentric explanation and disproved Ptolemy's theory. theory.

Was the Was the first to use a telescopefirst to use a telescope to look at objects in to look at objects in the sky and made the sky and made 2 discoveries2 discoveries with the telescope with the telescope that helped support the heliocentric theory. that helped support the heliocentric theory. 1. He saw 1. He saw four moons revolving around Jupiterfour moons revolving around Jupiter, ,

which proved that not everything in the sky revolves which proved that not everything in the sky revolves around Earth. around Earth.

2. He discovered that 2. He discovered that Venus goes through Venus goes through phasesphases similar to moon phases which could not be similar to moon phases which could not be explained if Earth were at the center of the universe.explained if Earth were at the center of the universe.

CheckpointCheckpoint What 2 discoveries made by Galileo What 2 discoveries made by Galileo

supported the heliocentric description supported the heliocentric description of the solar system?of the solar system?

Circles?Circles?

Copernicus and Galileo were both right, Copernicus and Galileo were both right, the the Sun is at the center of our solar Sun is at the center of our solar systemsystem, but Copernicus still falsely , but Copernicus still falsely believed the orbits of the planets were believed the orbits of the planets were circles just like Ptolemy believed. circles just like Ptolemy believed.

Tycho Brahe, a Danish astronomer Tycho Brahe, a Danish astronomer observed the positions of the planets for observed the positions of the planets for about 20 years and gathered a lot of data. about 20 years and gathered a lot of data.

Johannes Kepler (1600)Johannes Kepler (1600) Kepler, a German mathematician, used Kepler, a German mathematician, used

Brahe's data to study the planet's orbits Brahe's data to study the planet's orbits thinking at first that the orbits were all thinking at first that the orbits were all circles. circles.

He discovered, through trying to figure out He discovered, through trying to figure out the exact orbit of Mars, that the the exact orbit of Mars, that the orbit of orbit of each planet is an ellipseeach planet is an ellipse. .

Ellipse=an elongated circle or oval shapeEllipse=an elongated circle or oval shape

ellipse

Isaac NewtonIsaac Newton

Newton was an English scientist who Newton was an English scientist who concluded that 2 factors combine to keep concluded that 2 factors combine to keep the planets in orbit: the planets in orbit: inertia and gravityinertia and gravity..

Inertia and GravityInertia and Gravity

Galileo had discovered inertia, which is the Galileo had discovered inertia, which is the tendency of a moving object to continue in tendency of a moving object to continue in a straight line or a stationary object to stay a straight line or a stationary object to stay in place. (more mass=more inertia)in place. (more mass=more inertia)

Newton while watching an apple fall from a Newton while watching an apple fall from a tree discovered gravity which causes tree discovered gravity which causes objects in space to pull toward one objects in space to pull toward one another. another.

Planets are in orbit around the sun because Planets are in orbit around the sun because the sun's gravity pulls on them while their the sun's gravity pulls on them while their inertia keeps them moving ahead. inertia keeps them moving ahead. Therefore, the planets keep moving around Therefore, the planets keep moving around the sun and end up in orbit.the sun and end up in orbit.

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What shape are the orbits of the What shape are the orbits of the planets? How was the discovery of planets? How was the discovery of this orbit shape made?this orbit shape made?

What 2 factors work together to keep What 2 factors work together to keep the planets in orbit around the sun?the planets in orbit around the sun?

Other discoveries...Other discoveries... Ancient greeks only knew of Mercury, Venus, Ancient greeks only knew of Mercury, Venus,

Earth, Mars, Jupiter and Saturn, we now know of Earth, Mars, Jupiter and Saturn, we now know of Uranus, Neptune and a handful of dwarf planets Uranus, Neptune and a handful of dwarf planets including Pluto. including Pluto.

As technology is advancing, our understanding As technology is advancing, our understanding of the solar system continues to change thanks of the solar system continues to change thanks to the use of telescopes and space probes to to the use of telescopes and space probes to explore the unknown.explore the unknown.