Unit D: The Earth in the Universe

What causes light shows in the sky?

1. Get Set to Explore


  • atmosphere: The mixture of gases that surrounds Earth.
  • aurora: A set of shimmering bands of light that sometimes appears in the sky at night; another name for an aurora in the Northern Hemisphere is the northern lights.
  • electron: A negatively charged particle with a small mass; electrons are part of atoms and also can separate from atoms and move through space on their own.
  • latitude: A measure of distance north or south on Earth, starting at the equator.
  • magnetic field: Area near a magnet where a magnetic force can be detected.

Building Background

  • Ask students if they have ever seen the northern lights. If so, elicit descriptions from volunteers. If not, you might show students pictures—perhaps printouts from the simulation. Explain that in the simulation they will learn what causes the northern lights.
  • Review the definition of atmosphere with students, and talk about the gases that make up the atmosphere. If necessary, remind them that the atmosphere is made mainly of nitrogen and oxygen. Point out that these gases are found throughout the atmosphere—close to Earth and as it thins out into outer space.
  • Go over the definition of magnetic field with students. Let them share what they know about Earth's magnetic field. Write down their ideas on the board to discuss shortly.
  • Introduce the idea that the Sun gives off charged particles, including electrons, and review the definition of this word. Explain that the stream of charged particles the Sun gives off is called the solar wind. The solar wind varies in strength at different times.
  • Go over the remaining vocabulary words and their definitions. Then, referring to the previous discussion about the northern lights, put forward the Discover! question. Point out that the vocabulary terms introduced give hints about the answer. Let students work together in groups to address the question. After four or five minutes, have the groups share their hypotheses. Write them on the board to refer to later.

2. Guide the Exploration

  • Have students launch the Discover! Simulation. Before going on to Step 2, ask the class to return to their hypotheses for answering the Discover! question and to revise their answers based on new information that they have.
  • As students continue the simulation, point out that they can move their cursor over the controls and over different parts of the diagram to learn more about each.
  • Students should spend some time experimenting with the controls to see which conditions cause the aurora to occur in different locations. Remind students to take notes on what they learn. Let them revise their hypotheses about what causes the northern lights, before going on to Step 3.

3. Review/Assess

  • Invite a volunteer to read Step 3's Wrap-up text aloud to the class. Help students put together the following information. The solar wind sends out ‘gusts’ of electrons. Moving electrons act like tiny magnets, and so they are pulled in to Earth's magnetic field. As stated, Earth's magnetic field is strongest near the North Pole and the South Pole. Therefore, more electrons enter the atmosphere near the poles. As the electrons are pulled through the atmosphere, they collide with the molecules of nitrogen and oxygen gas there. When this happens, the gases give off light. We see the light as shimmering color in the sky—the aurora.
  • Pose the Extension question: Why do you think it is easier to see auroras during winter?

If time permits, present students with the following questions:

  • Inquiry Skill Infer Imagine you have observed the northern lights in a place where they are not usually visible. Based on what you have learned about how the northern lights form, what do you infer might have happened to cause the unusual light show? Answer: There might have been a very strong solar wind. This could cause the northern lights to form farther from the poles than they usually do.
  • Critical Thinking Synthesize What is one reason the northern lights shimmer? Answer: Like winds on Earth, the solar wind might vary in intensity from one minute to the next. This could cause the northern lights to shimmer.

4. Reaching All Learners

On Level: Logical and Visual Learners

After you go over the answer to the Discover! question, have logical and visual learners work together to make illustrated and labeled cause-effect diagrams to summarize the information. Review the diagrams for accuracy, and let students revise them, as necessary. Then have students post their diagrams for their classmates to study to reinforce the concepts.