Lesson 35: Day, Night, and Earth's Rotation

Earth's rotation produces the cycle of day and night and the Sun's apparent daily motion. A globe and lamp model connect this pattern with sunrise, sunset, and differences in local time.

Key Ideas

  • Earth spins, or rotates. Its rotation gives most places a repeating pattern of day and night, about every 24 hours.
  • The Sun appears to move across the sky mainly because Earth is turning.
  • The Sun usually rises on the eastern side of the sky and sets on the western side. The exact spots change during the year.
  • Places use time zones because different parts of Earth face the Sun at different times.
  • The pattern of daylight and darkness affects the daily activities of people and other living things.

Vocabulary

  • Rotation: The spinning of the Earth on its axis
  • Axis: The imaginary line through the center of the Earth, from the North Pole to the South Pole, around which it spins
  • Horizon: Where the sky appears to meet the Earth when you look straight out
  • Day-Night Cycle: The repeating pattern of daylight and darkness as Earth turns.
  • Sunrise: When the Sun appears above the horizon as a place on Earth turns into daylight.
  • Sunset: When the Sun disappears below the horizon as a place turns away from daylight.

Hands-On Activity: Model Day and Night with a Globe and Lamp

Set up a lamp on a stand near the center of the room and a globe on a small table about ten feet away. Darken the room so one side of the globe is clearly lit and the other is in shadow. Stick a rice grain near the equator with a dab of toothpaste and name him Joe.

Steps

  • Slowly turn the globe counterclockwise as viewed from above the North Pole while students watch closely.
  • Have them describe what Joe sees at each stage: sunrise, midday (sun highest), sunset, nighttime.
  • Add a second rice grain for Sally in California, west of Joe. Turn the globe to compare when the two locations enter daylight. Local sunrise and clock-time differences depend on longitude, latitude, season, and time-zone conventions.

Discussion Questions

  1. What do you think causes day and night?
  2. When Joe's side of the Earth faces away from the sun, what is he probably doing? Bonus: is it ever nighttime over the whole Earth at once?
  3. Would Joe in Florida and Sally in California see the sunrise at the same time? Why or why not?
  4. What real-world evidence could prove the Earth is actually spinning?
  5. If someone said the sun circles the Earth instead, what problems would that idea run into?
  6. What part of your daily life is connected to the Earth's rotation?

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