GROUP SIZE: Large
TIME: 45 minutes
TYPE OF ACTIVITY: Teacher/Student Demonstration TEACHING STRATEGY Guided Discovery Discussion
CONCEPTS: Earth Rotation Satellite Track Axis Tilt
SKILLS: Observation Inference Interpreting Data
Objective: To demonstrate that satellites pass over different parts of the Earth on each revolution because the Earth is rotating beneath it.
Materials: Yardstick; large balloon (light in color and able to inflate to at least 15″ in diameter or larger (circular in shape); two rubber bands; two felt markers (one black and one red); one large map of the world (wall map)
- Inflate the balloon. Tie it off with a rubber band.
- With a black felt marker, mark the North Pole (N) at the nozzle end and the South Pole (S) directly opposite
- Lay the yardstick on the table and line up “N” and “S” Poles. Have a student support the balloon while you draw a straight line of longitude from “N” to “S” Pole with the black felt marker.
- Turn the line of longitude perpendicular to the yardstick. Now support the balloon and ask a student to draw a line of latitude around the exact center of the balloon with a black felt marker. Ask the class which line of latitude this represents.
- Refer to the world map and locate 80° W longitude and 29° N latitude. Put a red X on that spot. Ask them where this is.
- Ask the class if anyone knows what the tilt of the earth‘s axis is. (23 1/2°)
- Approximate this tilt using the yardstick as a guide.
- Ask someone to hold the red felt marker on the red X while another student rotates the balloon to form a complete circle keeping the proper degree of inclination by using the yardstick below, and his or her line of sight.
Ask such questions as these:
- What does the balloon represent?
- What does the line of latitude represent?
- How many times does the orbital path cross the line of latitude?
- What would be the land mass crossed south of the line of latitude? Make a rough sketch of that land mass on the balloon.
- What other land masses would be crossed by the orbital path? Sketch those land masses, also.
- Where would be good locations for tracking stations?
You can have the students place dots to represent them on the balloon and have them record the location, the latitude and the longitude of several. Talk with the class about what things have to be considered before putting tracking stations in certain places.