1. Part 1: Planets and SS models Part 2: Kepler’s Laws of Motion
Name:______________________________________________
Part 1: Planets and SS models Part 2: Kepler’s Laws of Motion
Intro to
Planets and Planetary Motions!

2. What is the difference between revolution & rotation?

3. Our solar system is made up of : Planets, Dwarf Planets Asteroids, Comets, all of which orbit our Sun All formed from the collapse of the Solar Nebula (Which also formed our Sun)!

4. Planets are Categorized by (1) Terrestrial (made of dense rock) (2) Jovian (Made of lighter Gas and Ice)

5. All Planetary Data can be retrieved in your ESRT. A
All Planetary Data can be retrieved in your ESRT! A.)Which Planet could float in water? (Density)_____ B.) Which planet is the largest?(Equatorial Diameter)____ C.) Which planet’s day is longer than its year!? (Rotation/day vs. Revolution/year)_______

6. Planetary Sizes compared to the Sun to scale
Planetary Sizes compared to the Sun to scale! The further you go out in our solar system, the further the planets become from one another! (See mean distances from Sun in ESRT for each planet)
Terrestrial Planets move faster in orbit than Jovian Planets (see ESRT) WHY? As distance from the sun increases, gravity _____, decreasing speed

7. Geocentric Model (Earth-Centered) The Earth was fixed (did not rotate) All objects revolved around the Earth

8. Solar System Models
1.) Geocentric Model -proposed by Aristotle ( BC)
explained observations of:
-sunrise/sunset,
-moonrise/moonset
-apparent movements of the stars
-COULD NOT Not Explain:
1.) Motion of a Pendulum
2.) Retrograde motion (when we pass another planet in our orbit and it appears to move backward)

9. Foucault’s Pendulum : Provides evidence for Earth’s rotation
The ball swings back and forth, knocking the pegs over a period of 24 hours as earth rotates.
Pendulum Animation

10. Retrograde Motion: Mars Retrograde NASA Link
Planets revolve around sun in the same direction, but not at the same speed
Result: Earth passes planets in orbit
The planet will then appear to be moving in the opposite direction/backward over the course of the time we pass it in orbit (Can be seen over 2 months time)
Mars in Retrograde!
Retrograde Animation

12. 2.)Heliocentric Model-Our Current Model
*Sun is at the center of the solar system
- all the planets and comets revolve around the sun counter clockwise
Proposed by Copernicus ( )
Stars only appear to move because Earth revolves around the Sun!
Moons revolve around their planets

13. GEO = EARTH
HELIO = SUN
CENTRIC = CENTER

14. Kepler’s Laws of Planetary Motion (Responsible for the Information on the “Motions of Planets” in your review book!)

15. What shape do you believe the orbits of planets most closely resemble?

16. Kepler’s Three Laws of Motion
1. Orbits of the planets are Elliptical in shape (slightly eccentric) with the sun as one of the focal points of the ellipse.
2. Each Planet revolves around the sun at varying speed due to the eccentricity of their orbit. Equal areas of the ellipse will be covered in equal amounts of time due to this change in speed.
3. There is a proportional relationship between a planet’s orbital period and its mean distance to the sun.

17. First Law – Elliptical Orbits
Eccentricity is how stretched out the planet’s orbit is. The further the focal points are in an ellipse, what happens to the eccentricity?___________

18. If the Sun is always one of the foci, and we have an elliptical orbit, does our distance to the sun change over the course of one year? (one revolution)__________ Aphelion: Further Perihelion: Closer

19. ESRT: pg. 1 : Calculating “E”
eccentricity = dist. between foci length of major axis
Major axis: the longest
straight-line distance
across an ellipse
(longest distance)

20. Q: And the most eccentric? ___________:___________
There are no units for Eccentricity of Orbit (pg. 15 ESRT)
The scale: 0 – 1
0: Perfect circle
1: Straight Line
Q: Which planet in our solar system has the smallest eccentricity? (most circular orbit? _______________: _____________
Q: And the most eccentric? ___________:___________

21. Eccentricity data can be found for each planet on pg 15 ESRT

22. 2nd law: Speed ↑ as distance from sun ↓
Q: When is Earth moving the fastest?__________
Slowest? __________

23. 2nd Con’t: Equal Areas (colored) will be swept out in equal amounts of time- When a planet moves slower, it covers less distance in orbit, but an equal area in the orbit itself and vice versa

24. Third Law – “Harmonic Law”
the farther a planet is from the sun, the longer its period of revolution (the longer it takes to go around the sun

26. Comets also follow Keplar’s Laws of gravitational attraction and speed : At what point would Halley’s comet be traveling the fastest?

28. How to draw an Ellipse

29. Newton’s Universal Law of Gravitation
the force of gravity between any two objects is directly related to the masses (m) of the two objects
but inversely related to the square of the distance (r) between the centers of the two objects

30. Mass: larger the objects, the greater the force of gravity between them
Distance: greater the distance between the two objects, the less the force of gravity pulls on them
Simplified:

32. Question:
If the Earth's distance from the Sun were doubled, the gravitational attraction between the Sun and Earth would be?
a. one-ninth as great
b. nine times as great
c. one-fourth as great
d. four times as great
Answer C* Gravitational force= 1/ d 2

33. A planets orbit is a balance between inertia (would make planet travel in straight line) and gravity (would pull earth into the sun)