1. Chapter 24.1 Planet Earth

2. Learning Targets
Recognize that Earth is a modified sphere, and describe the evidence for this conclusion
Explain what causes Earth’s magnetism and the effects that magnetism has on the Earth
Describe Earth’s rotation on its axis
Describe Earth’s revolution around the Sun

3. Gravity causes planets:
Spheres and Orbits
Gravity causes planets:
To be roughly spherical
To orbit in ellipses
To hold onto their matter

4. Gravity Force of attraction between ALL objects
Affected by mass and distance
More mass  more gravity
Farther apart  less gravity
Weight changes; mass does not
You weigh less on Mt. Everest
You weigh more on Jupiter

6. The Earth has more mass than a person or a cannonball

7. Evidence for round Earth
Pictures
Horizon
Logic
Measurements

8. Eratosthenes 200 B.C. Calculations
Eratosthenes was a Greek scholar that lived in B.C. in Alexandria (Egypt). He received word that on that summer solstice day the sun is reflected perfectly in a deep well in Syene. But at the same time and same day, in Alexandria, the sun wasn’t reflected perfectly in the same type of well. Why? It occurred to him that the only way that could have happened is if the earth was not flat. Using simple trigonometry, he managed to calculate the radius and diameter of the earth.

9. Magnetism Swirling of liquid metal creates electricity
Outer core is liquid iron and nickel
Electricity creates a magnetic field
Magnetic field protects Earth from solar wind
Magnetic poles roughly line up with geographic poles

11. Earth’s Motions
Axis – Imaginary line passing through both North and South Poles
Rotation – Earth spins around its axis
Revolution – At same time Earth rotates on its axis, Earth also orbits around the Sun
A pendulum set in motion, will not change its motion, so it will not change the direction of the swinging. However, Foucault observed that his pendulum did seem to change direction. He knew that the pendulum itself could not change its motion, so he concluded that the Earth, underneath the pendulum was moving.

12. Rotation Earth rotates every 24 hours
Causes day and night cycles
Creates need for time zones
Confirmed by Leon Foucault’s pendulum
A pendulum set in motion, will not change its motion, so it will not change the direction of the swinging. However, Foucault observed that his pendulum did seem to change direction. He knew that the pendulum itself could not change its motion, so he concluded that the Earth, underneath the pendulum was moving.
At equator, Earth rotates at speed of 1,700 km/h, but pole’s speed is nearly nothing

13. Revolution
Earth revolves around the Sun once every year days or 1 year.
Seasons and day length are affected by tilt of Earth’s axis °
One complete revolution takes days, or one year. The Earth revolves around the Sun because gravity keeps it in a roughly circular orbit around the Sun. The Earth’s orbital path is not a perfect circle, but rather an ellipse, which means that it is like a slight oval in shape. Speed increases the closer Earth is to the sun and decreases the farther it is from the sun.
We are closer to the Sun at perihelion (147 million kilometers) on about January 3rd and a little further from the Sun (152 million kilometers) at aphelion on July 4th.

14. The rotation of the Earth

15. What degree is the Tropic of Capricorn and Tropic of Cancer? 23.5

16. During the Northern hemisphere summer the North Pole points toward the Sun, and in the Northern hemisphere winter the North Pole is tilted away from the Sun

17. What is the season?