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Universal Discoveries

The Universe

Ancient Ideas

● Ancient Greeks like Aristotle developed a geocentric model.

● Geocentric: Earth is in the center of the universe and the sun, moon, and planets revolve around it.

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Geocentric Model

What’s wrong with this idea?

● The geocentric model couldn’t explain retrograde motion.

● Retrograde Motion: ●  Planets like Mars look like they drift from side to side rather

than moving in one ‘straight’ line ●  An illusion caused by earth passing the slower moving outer

planets – Looks like the outer planets start to move backwards

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Retrograde Motion

New(ish) Ideas -- Copernicus

●  1473-1453 ● Earth is a planet just like the

others ● Developed the heliocentric

model. ● Heliocentric: ●  Earth revolves around the sun.

● This was a VERY controversial idea. ●  Why?!

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Heliocentric Model

New(ish) Ideas -- Brahe

● 1546-1601 ● Did not believe the

heliocentric model ● Thought stars should

demonstrate parallax ● Parallax: The difference in

position of an object viewed along two different lines of sight

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Parallax

New(ish) Ideas -- Kepler

●  1571-1630 ● Developed 3 laws of planetary motion

1.  Law of Ellipses 2.  Law of Equal Areas 3.  Law of Periods

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Kepler’s 1st Law: Law of Ellipses

● Orbits are shaped like an ellipse with sun as one focus

Ellipse

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Ellipse

●  Major Axis ●  Minor (semi-major) axis

Kepler’s 2nd Law: Law of Equal Areas

● A planet sweeps out an equal area in equal time no matter how fast it is moving. ●  Perihelion-closest to the sun ●  Aphelion- farthest from the sun

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Kepler’s 2nd Law: Law of Equal Areas

Kepler’s 2nd Law: Law of Equal Areas

●  It is implied from Kepler’s 2nd Law that a planet moves faster when it is closer to the sun and slower when more distant.

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Kepler’s 3rd Law: Law of Equal Periods

● The farther away a planet is from the sun, the longer it takes for one complete period.

●  1 astronomical unit (1 AU) is the average distance from sun to Earth ○  What are you noticing about

the different orbits? ○  Which idea might this

concept help reinforce?

New(ish) Ideas -- Galileo

● Created telescope ● Observed Jupiter’s moons ●  Saw planets are spheres ● Moon surface ●  Sun spots ● House arrest ● http://www.youtube.com/watch?v=-mwKEmqK8dI ● http://www.youtube.com/watch?v=RIRs6fwRjpM

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New(ish) Ideas -- Newton

●  1642-1727 ● Law of Universal Gravitation: Gravity keeps planets

from flying away ○  Mass is proportional (Mass goes up, gravitational force goes

up) ○  Longer the radius, weaker the gravitational pull.

● http://www.youtube.com/watch?v=vEaZkCX3Z-8