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? Has to do with orbital distance from the Sun

7. Geocentric Model Early model of the Solar System…problems?l

8. Solar System Models
1.) Geocentric Model –Earth was the center of the universe (All celestial objects revolved around Earth -proposed by Aristotle ( BC)
-explained observations of sunrise/sunset,
moonrise/moonset & 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 : Evidence for Earth’s rotation
The ball swings back and forth, knocking the pegs over. It will also move in a circle as the Earth rotates at 15degrees/hour.

10. 2.)Heliocentric Model- The correct one!
*Sun is at the center of the solar system
-and 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!

11. GEO = EARTH
HELIO = SUN
CENTRIC = CENTER

12. Retrograde Motion
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
Mars in Retrograde!
Retrograde Animation

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. Astronomical Unit - the average distance between the Earth and the Sun
1 AU = 93 million miles or 147 million km
What do you notice about Distance vs. Period of Revolution around the sun in your ESRT?
__________________________________________________________________________

25. 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 – common sense…why?)
Kepler stated this using the formula
P² = D³, where P is the period of revolution (in Earth years) and D is the distance from the sun (in AU’s) (pg. 15)

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

29. How to draw an Ellipse

30. Newton’s Universal Law of Gravitation
the force of gravity between any two objects is directly related to the masses of the two objects
but inversely related to the square of the distance between the centers of the two objects
Change in force = 1/distance²

31. Simplified:
The larger the objects, the greater the force of gravity between them
Also, the greater the distance between the two objects, the less the force of gravity pulls on them

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)