What is a Cycle?
The Tilted Earth TEK 8.7A the student knows the effects resulting from cyclical movements of the Sun, Earth, and Moon. The student is expected to model and illustrate how the tilted Earth rotates on its axis, causing day and night, and revolves around the sun causing changes in seasons.
Outline Notes
Rotation - Earth spinning on its axis A. Earth s rotation on its axis causes day and night B. It takes 24 hours for Earth to rotate once on its axis C. Earth rotates in a counterclockwise direction D. Earth rotates at about 1,600 kilometers per hour Rotation Animation
A. Earth travels (revolves) around the sun B. One complete revolution around the sun equals a year Revolution The movement of one object around another object C. It is a curved path (elliptical) followed by Earth as it moves around the Sun D. Earth s orbit is about 365 ¼ days (Leap year every four years)
Become the Earth! Stand in place, and make one complete turn (You have just rotated) Take a trip around your chair (You have just revolved) Do you think you can rotate and revolve at the same time? Try it now!
Tilted Earth Causes Earth rotates On its axis revolves Around the sun causing causing Day and night Years
So now you understand day and night What about seasons?
Name the seasons Need a volunteer for the board! List the seasons on it Now, everyone tell this person the characteristics of each season Ideas: temperature, what is the weather like, are things being born, growing old, etc.
So why do we have seasons?
First things first How the Earth is divided?
Hemispheres of Earth:
The Equator:
Earth s Axis:
Tilt A Whirl! 1. Earth has seasons because its axis is tilted as it revolves around the sun 2. If Earth s axis were straight up and down, temperatures would remain constant year round (no seasons)
Seasons 1. The Earth's axis is tilted by 23.5 2. The Earth s tilt causes uneven heating by the sun
Why is it warmer near the equator than near the poles? 1. At the equator - sunlight hits Earth s surface more directly 2. Near the north and south poles - sunlight hits Earth s surface at an angle (energy from the sun is spread out over a greater area)
Direct vs. Indirect Light
Indirect Rays When the northern hemisphere is leaning away from the sun, the rays coming from it hits this part of the Earth at a smaller (slanted) angle compared to other parts of the world This means that with indirect rays there is the same amount of energy spread over a larger area of the earth therefore it receives less energy (heat)
Direct Rays 1. The light is more concentrated, more of a straight line 2. Therefore, the heat is more concentrated too! 3. Explain why it is hotter at the equator in your notes now.
Now with a globe! Winter Sun (Indirect) Summer Sun (Direct)
Earth s Tilted Axis A. Earth s axis is tilted away from the sun for part of the year and toward the sun for part of the year When tilted toward the sun summer When tilted away from the sun - winter Note: Summer and winter are not affected by changes in Earth s distance from the sun.
B. Another thing about the Earth s tilt: Earth s axis always points in same direction (towards Polaris - the North Star)
Another view: Which diagram shows which season for the northern hemisphere?
Label your diagram now: Add what is missing:
Look at the direction of the axis during each season. Does the axis tilt direction ever change?
Misconception Alert! Seasons are NOT caused by the changing distance the Earth is from the Sun. The Earth travels in an elliptical orbit, so the distance does vary but not enough to cause the change in temperature associated with seasons!
When the southern hemisphere is experiencing summer, the northern hemisphere has winter (so what does this mean for Christmas in Australia?)
HW Read and Response: Read pgs 224 232 in your textbook. This is the first step. Second step is to answer the questions on p. 233