1. The planets
12/1/14

2. The planets
What is the difference between the Terrestrial and the Jovian Planets?
Remember:
Terrestrial Planets
Mercury, Venus, Earth, Mars
Small
Close to the Sun
Dense/Solid
Jovian Planets
Jupiter, Saturn, Uranus, Neptune
Large
Far from the Sun
Gas/Not dense

3. Motions of the Planets speeds 225 rotate revolve
Each of the 8 planets of our Solar System are constantly moving in many different directions and __________
First, they are moving with the Solar System around the Milky Way Galaxy in periods of about _______ million years!
They also __________ around an imaginary axis and _________ around the Sun
speeds
225
rotate
revolve

4. Motions of the Planets

5. Planet Rotation rotation period day
Planets spin on an imaginary axis in a motion called __________
The _________ of rotation is the amount of time it takes for a planet to make one spin around its axis – this determines the length of the planets ______
rotation
period
day

6. Planet Rotation

7. Planets rotation
Using the Solar System Data Table in your ESRT, answer the following questions about the rotations of the planets:
What is the length of a day on Mars? ________________________
Which planet has the shortest period of rotation? _____________
What is the exact length of rotation for the Earth? _____________________
How long is one day on Saturn? ____________________________
Which planet has the longest period of rotation? ______________

8. Geocentric vs heliocentric Models
What is the difference between the Heliocentric and the Geocentric Models of the Solar System?
“Geo” means Earth  Earth centered model
“Helio” means Sun  Sun centered model X0

9. Geocentric Model

10. Heliocentric Model

11. Initial Proof
Venus goes through phases just like our moon!

12. Initial Proof

13. Planet Revolution revolution orbit counterclockwise year
A planet’s ____________ is its movement around the Sun in a path called an _______
The planets revolve around the Sun in a ______________________ direction
The amount of time it takes a planet to revolve around the Sun is considered that planets _______
orbit
counterclockwise
year

14. Planet Revolution

15. Planet revolution
Using the Solar System Data Table in your ESRT, answer the following questions about the revolutions of the planets:
How long does it take the Earth to revolve around the Sun? _________________________
What do we do to account for the lack of a full day in our revolution? _______________________________________
Before looking at your Reference Table – which planet would you expect to have the shortest period of revolution? Why?
Which planet does have the shortest period of revolution? __________________
Before looking at your Reference Table – which planet would you expect to have the longest period of revolution? Why?
Which planet has the longest period of revolution? __________________

16. Johannes Kepler
Kepler was a 17th century German mathematician, astronomer, and physicist
He was the first to discover that planets do not orbit in perfect circles around the Sun

17. Kepler’s Laws of motion
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After studying the planets to the point where he almost went insane, Kepler made an incredible discovery that he defined in 3 Laws (we are only going to discuss 2 of them)

18. Kepler’s 1st Law of motion
ellipse
The orbit of a planet is an __________ with the Sun at one of the two ______
An ellipse is an oval shaped orbit
foci

19. Kepler’s 2nd Law of motion
speed
A planet’s orbit will change _________ depending on its distance from the Sun
When the planet is closest to the Sun, it will be moving _____
When the planet is farthest from the Sun, it will be moving _______
fast
slow

20. Kepler’s 2nd law of motion
PLANETS MOVE FASTER CLOSER TO THE SUN!

21. Let’s look at the elliptical orbit of a planet…
Major Axis
Planet
Sun
Minor Axis
Foci
The major axis is the longer line that cuts through the two foci!

22. Eccentricity eccentricity eccentric
The ________________ of an ellipse is the degree of “ovalness” – or how oval-shaped it is
The more “flattened” the orbit is, the more _____________ it is
eccentric

23. Eccentricity
Eccentricity is a measured value that always falls between the numbers __ and __
A perfect circle has an eccentricity of _____
What do you think the eccentricity of a straight line would be? 1
zero

24. Eccentricity Formula
Eccentricity of ellipse = 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑓𝑜𝑐𝑖 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑚𝑎𝑗𝑜𝑟 𝑎𝑥𝑖𝑠
Distance between foci
Length of major axis

25. Eccentricity formula
Determine the eccentricity of the following ellipse:
3.578 cm
5.897 cm

26. Eccentricity of Planetary Orbits
Using the Solar System Data Table in your ESRT, answer the following questions about the eccentricity of the planetary orbits:
What is the eccentricity of Earth’s orbit? ____________________
Which planet has an orbit closest to a perfect circle? __________________
Which planet has the most eccentric orbit? __________________
What is the eccentricity of the moon’s orbit around the Earth? ___________________________

27. Inertia and Gravity inertia motion speed
The planets stay in their orbits because of a balance of two things: _________ and gravity
Inertia is the concept that an object at rest stays at rest and an object in motion stays in motion unless acted on by another force
Inertia acts on the planets by maintaining the _________ and ________ at which they revolve
However, the force of gravity affects this motion!
inertia
motion
speed

28. Inertia and Gravitation
attractive
Gravitation is the ____________ force that exists between two objects
The gravitation force depends on two things:
The ____________ between the objects
The __________ of the two objects
distance
masses

29. Gravitational Force higher
The larger the object, the _________ its gravitational pull

30. Gravitational Force higher
The closer two objects are together, the _________ the gravitational pull
higher

31. Inertia and Gravitation
So this is why planets move faster when they are revolving closer to the Sun and slower when they are revolving far from the Sun
The Sun is pulling them in toward it causing the planet to move faster!