Chapter 24.1 Planet Earth

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

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

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

The Earth has more mass than a person or a cannonball

Evidence for round Earth Pictures Horizon Logic Measurements

Eratosthenes 200 B.C. Calculations Eratosthenes was a Greek scholar that lived in 275-194 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.

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

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.

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

Revolution Earth revolves around the Sun once every year 365.24 days or 1 year. Seasons and day length are affected by tilt of Earth’s axis - 23.5° One complete revolution takes 365.24 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.

The rotation of the Earth

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

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

What is the season?