2. What is rotation? Spinning on an imaginary axis Period of rotation is the time it takes for a planet to make 1 spin on its axis =length of a planet day

3. What is revolution? A planet’s movement around the sun is a path called an orbit Period of revolution is the time it takes for a planet to orbit around the sun = length of a planets year

4. What is the shape of the planets’ orbits around the Sun? Ellipse – Oval in shape. It has 2 fixed points called foci

5. What is meant by eccentricity? The degree of “ovalness” of an ellipse Ranges from zero to one. –0 is a perfect circle, the closer to 1 the more oval –1 is a straight line

6. What is the formula for eccentricity? Example Eccentricity= distance between foci (d) Length of major axis (L) Eccentricity = __1.1 cm__ 4.7 cm = 0.234 Compare the eccentricity of this orbit to that of Saturn’s orbit.

7. Are the planets always the same distance from the sun? No, because of the elliptical shape of the planet orbits, they vary in distance from the sun during revolution.

8. What is perihelion? When Earth is closest to the sun. Since the Earth is closest to the sun it will have the largest apparent diameter during the year (look bigger) Greatest force of gravity between Earth and Sun

9. When is the Earth in Perihelion? During winter - January 3rd

10. What is aphelion? When Earth is farthest from the sun Since the Earth is farthest from the sun it will have the smallest apparent diameter during the year (look smaller) Least gravitational force between Earth & Sun

11. When is the Earth in Aphelion? During summer – July 4th

12. What two forces balance a planet’s revolution? The two forces that balance out the planet’s revolution would be:  Gravity & Inertia

13. What is inertia? An object in motion, stays in motion and an object at rest, stays at rest unless acted on by an outside force

14. What is gravity? An attractive force that exists between any 2 objects in the universe.

15. What effect does mass have on gravity? The greater the mass, the greater the force of gravity

16. What effect does distance have on gravity? The closer the object are to each other the greater the force of an object.

17. What is Kepler’s law of equal areas? A planet sweeps out equal areas in equal amounts of time A must = B

18. When does a planet have its fastest orbital velocity? When it is closest to the sun (perihelion- winter), because the gravitational pull is largest. At which location does this occur?

19. When does a planet have its slowest orbital velocity? When its farthest from the sun (aphelion- summer), because the gravitational pull is smallest. At which location does this occur?

20. 1)At which letter, does the apparent diameter of the sun appear the largest? 2)At which letter, does the apparent diameter of the sun appear the smallest? 3)What season occurs at letter A? 4)What season occurs at letter C? 5)What season occurs at letter B? 6)What season occurs at letter D? 7)What happens to the orbital velocity as you move from point A to C? 8)What happens to the orbital velocity as you move from point C to A? 9)What happens to the orbital velocity as you complete one revolution starting from point C? 10)What happens to the orbital velocity as you complete one revolution starting from point A?