Bellwork 1.Who is credited with the revolutionary model of a HELIOCENTRIC solar system? A. Aristotle B. Ptolemy C. Galileo D. Copernicus 2.The planets.

1

Bellwork

1. Who is credited with the revolutionary model of a HELIOCENTRIC solar system?

A. AristotleB. PtolemyC. GalileoD. Copernicus

2. The planets loop backwards in their orbits.A. TRUEB. FALSE

3. During which months is Earth closest to the Sun?

2

The story so far….• Ancient Greeks had a GEOCENTRIC model of the solar system

with Earth in center and Sun and planets in perfect circles.• Ptolemy add many epicycles to explain the looping of planets

during retrograde motion.• Galileo used a telescope to see phases of Venus, Jupiter’s

moons, rotating sunspots• Copernicus made a HELIOCENTRIC model of the solar system

with the Sun in the center so the planets were NOT looping backwards, Earth’s faster orbit was ‘passing’ the slower outer planets.

http://www.classzone.com/books/earth_science/terc/content/investigations/es2603/es2603page01.cfm3

4

Kepler’s Model of the Solar System

Tycho Brahe (1575)

After seeing the total eclipse on August 21, 1560, and became a master of careful astronomical OBSERVATIONS.

Lost part of his nose in a duel and replaced it with a metal one.

Made DETAILED naked eye observations of the motions of the planets.

In the course of 30 years, he had amassed the most accurate astronomical DATA of the day

5

Mathmatician - Kelper's mathematical skills were extraordinary.

He could not get Tycho's very careful observations to fit Copernicus’ model.

He constructed 3 Laws about planets orbits:

SHAPE, SPEED, TIME

Kepler ‘inherited’ the observations after the sudden death of Tycho

Johannes Kepler’s (1600)

6

Kepler’s 3 Laws of Planetary Motion

1st Law: Ellipses!

The SHAPE of the orbital paths of each planet is an ellipse (NOT a perfect circle)

(with the Sun not exactly in the center, but at one focus)

7

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::800::600::/sites/dl/free/007299181x/78778/Kepler_Nav.swf::Keplers%20Second%20Law%20Interactive 8

2nd Law: SPEED of the planet

An imaginary line connecting the Sun to any planet sweeps out equal areas in equal time.

Area 2

Area 1

90 days

90 daysPlanets have

variations in their orbital

speed 9

Kepler’s 3rd Law:

a planet’s orbital TIME is proportional to its distance.

P2 (years) = A3 (AU)

1 Astronomical Unit = The Earth-Sun Distance (93 million miles)

In other words……the farther away the planet, the longer its ‘year’

10

Kepler’s Third LawObject a (AU) P (year) a3 P2

Mercury 0.387 0.241 0.058 0.058

Venus 0.723 0.615 0.378 0.378

Earth 1.00 1.00 1.00 1.00

Mars 1.52 1.88 3.51 3.53

Jupiter 5.20 11.9 141. 142.

Saturn 9.54 29.5 868. 870.

Uranus 19.2 84.0 7,080. 7,060.

Neptune 30.1 165. 27,300. 27,200.

Pluto 39.5 248. 61,600. 61,500.

=

=

=

=

=

=

=

=

=

11

12

Heliocentric Solar System

Using data construct a model to show the correct SIZE and SCALE

Isaac Newton (1642 – 1727)

One of the most brilliant theoreticians to ever live.

Explained WHY the planets move as they do.

He formulated three laws of motion and the law of universal gravitation.

13

Newton’s 1st Law of Inertia:Objects in uniform straight line motion continue in straight line motion unless an outside force is applied to change their motion

Once in orbit, a planet will continue its orbital motion at constant velocity until an outside force (asteroid,

another planet?) acts on it to change its orbit.

14

Newton’s Second Law

The ACCELERATION (change in motion) of an object is directly proportional to the net FORCE acting on the object, is in the direction of the net force, and is inversely proportional to the MASS of the object.

a = Fnet

massOR

F = ma

WHY

15

Newton’s Third Law

Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object.

“To every action there is an equal and opposite re-action.”

Forces are interacting in PAIRS – one object on another

16

Law of Universal Gravitation

Mass attracts mass

221

R

MGMF

Gravity is the FORCE that causes objects to move!17