Name Class Tilted Earth Lab Why Do We Have Seasons? Purpose: In this investigation, you are going to figure out how the axis (or tilt) of the Earth, combined with the revolution (orbit) of Earth around the sun, determines the seasons. Materials: A globe (model of Earth) A crate A lamp A light bulb represents the sun Colored dots (already on the globe) that represent cities located at different latitudes in the Northern and Southern Hemispheres. Latitude measures the distance north or south of the Equator. Background Information: The Earth is not positioned straight up and down in space, it is tilted on an axis. The axis is an imaginary line running from the North to South poles. The northern part of Earth s axis is always tilted 23.5 towards the North Star (called Polaris). The Earth rotates (spins) on this axis all the time, turning around completely once every 24 hours. The rotation of Earth is counter-clockwise and is what causes day and night. The Earth also orbits around the sun at the same time it is spinning on the axis. The Earth revolves around the sun in a counter-clockwise motion and it takes Earth 365 ¼ days to make one complete revolution. This is one year. Set-Up: Sit at a table so that one group member is on each side of the lamp. If you only have 3 group members, skip the position that is closest to the outlet. Give the globe to the student sitting in position A and put the globe on the crate. Find the North Star above the windows (the north wall), and point the northern end of Earth s axis towards it. Be sure to keep the Earth s axis pointed toward the North Star as it revolves around the sun (light bulb) no matter what season it is! This is called parallelism because the Earth s axis is always parallel to itself no matter where it is in orbit around the sun.
Recording Data: As you complete this lab, use the diagram below to record information about Earth s position during each season. Seasons on Earth Diagram: For each position (A,B,C,D) make sure to: 1. Label the season on the line next to each letter. 2. Draw what Earth s axis and equator look like in each circle. 3. Shade the half of the Earth that is not being lit by the light bulb. A North Star B D C
Earth in Position A: Have the student that is in position A push the globe on the crate about 12 inches away from the light bulb. Make sure that the Equator is even with the middle part of the light bulb, then tilt the Earth s axis so that the North Pole is pointing toward the North Star. The axis of Earth should always be pointed in this direction. Draw the positions that the Earth s axis and Equator are located in on position A of the diagram (page 2) and label the season. Don t forget to shade the part of the Earth that is not being lit by the light bulb. One half of the Earth always receives light from the sun. Get down at eye level to the globe so that you can see the day-night line. The day-night line should line up with the North and South Poles when the globe is in this position. 1. Rotate Earth around once on the axis. This represents 24 hours. As you are turning Earth s axis, carefully observe when day turns into night in BOTH the Northern and Southern Hemispheres. What do you notice? Explain. 2. The red dot city and the green dot city on your model are equal distances (north or south) of the Equator. Compare the amount of sunlight that red dot city (mid-latitude North) receives compared to the green dot city (mid-latitude South). What do you notice? 3. Which area of the Earth is receiving the most direct sunlight? 4. When the Earth is in position A, the days are the exact same length in both the Northern and Southern Hemispheres. This is the beginning of the Solar New Year. A What is this special time called? C When does this event occur on our calendar? _
Earth in Position B: In a counterclockwise motion, move the Earth model ¼ turn to position B. Be sure that the axis remains pointing at the North Star as it orbits and while it is in position B. Draw the positions of Earth s axis and Equator in position B of the diagram on page 2. Label the season in the Northern Hemisphere on your diagram and draw the equator and axis of the Earth. Next shade what side of Earth that is not being lit by the light bulb. 1. Which hemisphere is receiving more direct sunlight? 2. Which hemisphere is receiving more indirect sunlight? 3. Get down on eye level so that you can see the day-night line. Rotate Earth s axis around completely one time. This is equal to 24 hours. (Remember that the axis still must be pointing to the North Star while you do this!) As you are turning Earth s counter-clockwise, carefully observe day turning into night in BOTH the Northern and Southern Hemispheres. Which hemisphere has a longer day? Which hemisphere has a shorter day? Explain. 4. The red dot city and the green dot city are equal distances (north or south) of the Equator. Compare the amount of direct sunlight that red dot city (mid-latitude North) receives compared to the green dot city (mid-latitude South). In other words, what is the difference in the angle of light that each city is receiving from the sun? What differences do you notice? 5. Rotate Earth s axis around completely (24 hours). What is happening to the amount of light received in the North Pole? What is causing this? Explain. 6. What can be said about the length of the day in the Northern Hemisphere when Earth is in this position in space? You may want to refer to your notes to help you out! 7. The Northern Hemisphere has the longest day and the Southern Hemisphere has the shortest day when Earth is in position B,. A What is this special time called in the Northern Hemisphere? C When does this event occur on our calendar? _
Earth in Position C: In a counterclockwise motion, move the globe a ¼ turn to position C. Be sure that the axis remains pointing at the North Star as it orbits and while it is in position C. Draw the positions of Earth s axis and Equator in position C of the diagram on page 2. Label the season in the Northern Hemisphere and draw the equator and axis of the Earth. Next shade what side of Earth that is not being lit by the light bulb. (Hint: In this position on your diagram you will not be able to see much light on the face of the Earth!) 1. Rotate Earth around once on the axis. This represents 24 hours. As you are turning Earth s axis, carefully observe when day turns into night in BOTH the Northern and Southern Hemispheres. What do you notice? Explain. 2. The red dot city and the green dot city on your model are equal distances (north or south) of the Equator. Compare the amount of sunlight that red dot city (mid-latitude North) receives compared to the green dot city (mid-latitude South). What do you notice? 3. Which area of the Earth is receiving the most direct sunlight? 4. When the Earth is in position C, the days are the exact same length in both the Northern and Southern Hemispheres. A What is this special time called in the Northern Hemisphere? C When does this event occur on our calendar? _
Earth in Position D: In a counterclockwise motion, move the Earth model ¼ turn to position D. Be sure that the axis remains pointing at the North Star as it orbits and while it is in position D. Draw the positions of Earth s axis and Equator in position B of the diagram on page 2. Label the season in the Northern Hemisphere on your diagram and draw the equator and axis of the Earth. Next shade what side of Earth that is not being lit by the light bulb. 1. Get down on eye level so that you can see the day-night line. Rotate Earth s axis around completely one time. This is equal to 24 hours. (Remember that the axis still must be pointing to the North Star while you do this!) As you are turning Earth s counter-clockwise, carefully observe day turning into night in BOTH the Northern and Southern Hemispheres. Which hemisphere has a longer day? Which hemisphere has a shorter day? Explain. 2. The red dot city and the green dot city are equal distances (north or south) of the Equator. Compare the amount of direct sunlight that red dot city (mid-latitude North) receives compared to the green dot city (mid-latitude South). What differences do you notice? 3. Rotate Earth s axis around completely (24 hours). What is happening to the amount of light received in the North Pole? What is causing this? Explain. 4. What can be said about the length of the day in the Northern Hemisphere when Earth is in this position in space? You may want to refer to your notes to help you out! 5. The Northern Hemisphere has the longest day and the Southern Hemisphere has the shortest day when Earth is in position B,. A What is this special time called in the Northern Hemisphere? C When does this event occur on our calendar? _
Analyze Your Results: Circle one: When Earth revolves around it s orbit, it moves in a [ clockwise / counterclockwise ] direction. 1. What are the two (2) reasons that cause Earth to have seasons? Explain using details! 2. What is an equinox and a solstice? When do they occur and what are their names? 3. How does the concentration of the sun s energy change during the summer and winter months? Explain. 4. In January, what would it be like in the SOUTHERN hemisphere in terms of length of day and season? Explain. 5. Describe two ways the Northern and Southern Hemispheres similar during the spring and autumn (fall): 6. Some planets, like Mercury, have barely any axis tilt at all. Would a planet with NO axis tilt have seasons? Why or why not? Explain.