Objectives: Students will: - explain the relationship between the sun and Earth - describe how the tilt and position of the Earth affects the seasons - explain differences in direct and indirect sunlight
Materials:
Black construction paper
Flashlights
Globe
Markers
Polystyrene foam balls or round fruit
Push pins
Rulers
Scissors
Toothpicks
Transparent tape
Narrative:
Activate prior knowledge about seasons and sunlight. Explain to students that the Earth orbits an ideal distance from the sun, and this affects the weather we experience here on Earth. Ask: What are the different seasons? Write the sequence of the seasons on the board for students’ reference: winter, spring, summer, autumn. Ask: What is the weather like during the different seasons? What is the same or different about the seasons? Prompt students to include similarities and differences in weather, temperature, and length of daylight. Write their ideas on the board. Then explain to students that the answer to that question is different for those who live in a different hemisphere, or half of the Earth.
Ask: What do you think causes the difference in seasons? What do you think causes the difference in what time it gets dark outside? Build background about what causes seasons. Use a globe and gesture to reinforce the vocabulary terms tilt and axis from the day and night lessons.
As the Earth travels along its orbit, it sometimes leans toward the sun and sometimes away from the sun. Display the diagram “Seasons” for students, and point to the parts of the diagram as you explain the following: If you live in the Northern Hemisphere, you live on the part of the Earth that is north of the Equator. When the Northern Hemisphere is tilted toward the sun, you experience summer. When the Northern Hemisphere is tilted away from the sun, you experience winter. Ask: How would this change if you lived in the Southern Hemisphere?
Group Activity:
Provide each group with one polystyrene foam ball, one marker, one flashlight, and two pushpins. Have groups choose who will hold the foam ball that represents the Earth and who will hold the flashlight that represents the sun. Ask the student holding the Earth to draw a circle around its middle to represent the Equator, and dots on the North Pole and South Pole. Have the third group member place a pushpin, representing a person, midway between the Equator and the North Pole, and another between the Equator and South Pole. Make sure students place both pushpins on the same side of their Earth. Tell students that the Earth moves around the sun in a circular orbit and is tilted on its axis. Explain that as Earth orbits the sun, it rotates on its axis, and the axis is always pointed in the same direction. Have the students representing the Earth and sun in each group stand approximately 5-7 feet apart. Dim or turn off the lights.
Use guided inquiry to have students investigate direct and indirect sunlight. First, have the student acting as the sun keep the flashlight pointed straight at the representation of Earth while the student holding Earth walks in a circle around the sun. The Earth should stop when the pushpin representing a person in the Northern Hemisphere can "see" the sun. Ask the student holding Earth to tilt the Earth so that the sun, without moving the flashlight, is shining directly overhead of the pushpin/person in the north. Ask: Is the sun more direct, or bright, for the person at the top or the person at the bottom of the Earth?Do you think it is warmer for the person at the top or the person at the bottom of the Earth? (top) Why do you think so? Address any student misconceptions.
Now ask the student holding Earth to orbit the sun, making sure to hold the tilt in the same direction until the tilt of the Earth is positioned so that the sun is directly overhead of the pushpin/person in the Southern Hemisphere. Ask: Is the sun more direct, or bright, for the person in the Northern Hemisphere or the Southern Hemisphere?Which person do you think feels warmer temperatures?Why?
Use guided inquiry to help students investigate the role of axis and tilt in the sun-Earth relationship. While the sun is still shining directly overhead of the pushpin/person in the Southern Hemisphere, have students locate where in the classroom, such as a wall or ceiling, the North Pole points to. Tape a black circle to the wall at that location to help students keep the axis pointed in one direction. Next, ask the Earth to resume orbiting the sun, while keeping the North Pole pointed at the black circle. Explain to students that the Earth is tilted one way and stays tilted the same way all the time. Have students stop the Earth after one-half of an orbit so that it is opposite of where it started. Then ask one group member to make it daytime for the “top” and “bottom” people. It should be night for them if the Earth has orbited correctly, so the student will have to spin the Earth. Finally, ask groups to move the Earth half an orbit around the sun again, making sure to keep the North Pole pointed at the black circle. Make sure the sun does not move. Also, ensure as the Earth orbits the sun, the axis does not change orientation and continues pointing to the black circle. Have a group member make it daytime for the “top” and “bottom” people.
Assessment Questions:
Does the sun shine more directly on the person on the top half of the Earth, or the person on the bottom half? Which person feels warmer temperatures? Which person is experiencing summer? Winter? How do you know? Is the sun brighter or more concentrated for the person in summer or the person in winter? Have a whole-class discussion about how the sun affects Earth’s seasons. Point out to students that the seasons are opposite for people on the top (north) of the Earth and on the bottom (south) of the Earth.
Ask:
When it is winter on the top (north) of the Earth, what season is it on the bottom (south) of the Earth? When it is winter on the bottom (south) of the Earth, what season is it on the top (north) of the Earth? How can we use angles to help others to understand seasons?