What causes the northern lights? When are they most visible? What creates the different colors? What do the auroras look like from space?

Aurora Borealis
What creates these shimmering celestial lights?

Insights

Folklore is rich with explanations for the stunning night-sky lights, the aurora borealis. Various cultures have explained them as dancing spirits or blood raining from the clouds. Aurora was the Roman goddess of the dawn. Boreal is a Latin word, meaning "north." Thus, the northern lights. In the Antarctic, the lights are called the aurora australialis, or southern lights.

The source of the auroras is the sun. The sun gives off high-energy charged particles (also called ions) that travel out into space at speeds of 200 to 440 miles per second. A "cloud" or gas of such ions and electrons is called a plasma. The stream of plasma coming from the sun is known as the solar wind. As the solar wind interacts with the fringes of the earth's magnetic field, the particles are "shocked" into flowing around the earth. Some of the particles are trapped by the earth's magnetic field. They follow the magnetic lines of force down to the ionosphere. The particles strike the gases in the ionosphere, causing them to glow, the same way electrons passing through the gases in a neon tube make a neon sign light up. The colors correspond to the different gases in the ionosphere. Oxygen atoms give off red and green light, depending on how high they are in the ionosphere. Nitrogen molecules give off blue and violet light.

The northern lights are always moving, like giant curtains of light weaving and swaying across the sky. This is caused by the constantly changing interaction between the solar wind and the earth's magnetic field. It is not unusual for the solar wind to generate 100,000 megawatts of electricity in a three-hour auroral display. This can cause temporary interference with power lines, radio and television broadcasts, and satellite-to-earth communications. By studying the auroras, scientists can learn more about the solar wind and how it affects the earth's atmosphere.

Connections

1. What are some examples of how we have used the sun's power? How might we use plasma power in the future?
2. Artificial auroras were created on a recent NASA shuttle mission. How did they do this? What might this lead to later that could be used on earth?

Vocabulary

aurora rapid and irregular displays of colorful lights in the night sky, created when the solar wind causes beams of electrons from the magnetosphere to strike the upper atmosphere, causing atoms and molecules to glow
electromagnetic spectrum arrangement of electromagnetic waves according to wavelength
ion an atom or group of atoms carrying an electrical charge
ionosphere part of the earth's atmosphere containing electrically-charged particles that reflect radio waves.
magnetic field a region of space wherein a detectable magnetic force exists at every point
plasma a state of matter in which all of the particles are electrically charged
solar corona the sun's upper atmosphere where the solar wind is created
solar wind charged particles, mainly protons and electrons, that flow out from the sun and sweep out into space.

Resources

Akasofu, S.I. (1982) The aurora: New light on an old subject. Sky and Telescope (Dec): 534.

Akasofu, S.I. (1989) The dynamic aurora. Scientific American (May): 90.

Maran, S.P., ed. (1992) The astronomy and astrophysics encyclopedia. New York: Van Nostrand Reinhold.

Additional sources of information:

NASA
Education Division
Mail Code F
Washington, DC 20546

NASA
Johnson Space Center
Media Services
Houston, TX 77058
(auroral photographs)

NOAA, E/GCI, Dept. 883
National Geophysical Data Center
325 Broadway
Boulder, CO 80303
(303) 497-3000
(print materials, slides, satellite images)

Community resources:

University astronomy department
Meteorologists

Main Activity

Use some common materials to discover if ions conduct electricity.

Materials

• beaker
  
• 1 meter of insulated bell wire
  
• distilled water
  
• 2-1.5-volt dry cells
  
• 3-volt flashlight bulb (microlamp)
  
• paper towels
  
• 1/2 cup sugar
  
• 1/2 cup salt
  
• wire cutters to strip insulation from wires

1. Cut the bell wire into three pieces and strip 1 cm of insulation from the end of each piece.

2. Connect the two batteries with one wire.

3. Connect one end of the remaining wire to a battery; connect the other end to the flashlight bulb. Attach the third piece of wire to the second battery and to the bulb.

4. Cut one wire in the circuit between the bulb and battery; remove 1 cm of insulation.

5. Place two bare ends of the wire into a beaker filled halfway with distilled water. How does the light react?

6. Dry off the ends of the wire; pour 1/4 cup of the salt on a paper towel. Put the wire ends into the salt. How does the light react?

7. Clean and dry the ends of wire again, sprinkle a few grams of sugar into the water, and place the ends of the wire into the water/sugar mixture. What happens to the bulb?

8. Replace the sugar water with plain distilled water. Add the salt. Does the light react?

Questions

1. Ions conduct electricity. What was it that freed the ions? How do you know?

2. Which solutions or mixtures did not produce ions?

3. How is this similar to the process that creates the northern lights? To the process that creates fireworks?

Mythology and folklore are used to explain many natural geographical features and/or events of nature. Create a time-travel story, play, or dance, which reveals the "ancient" belief about a natural phenomenon, along with the related scientific theory or principle. Some ideas for natural events include lightning, solar and lunar eclipses, and rainbows.

Make a miniature earth and its magnetic field by covering a bar magnet with some modeling clay, and then forming the clay into a sphere. Keeping the magnet upright, place the clay-earth model on a table. Cut a strip of cardboard to represent the equator, wrap it around the model, and tape the ends. Sprinkle iron powder or filings on the model. At what point do the lines build up? Is there a pattern? How do you think the filings would continue toward the southern pole?

Invite your friends to a "northern lights" party. Give each person a pack of wintergreen-flavored round candies. (Do not use the sugar-free kind.) Go into a very dark room or outside at night. Ask each person to bite down on two or three pieces of candy. (Keep your mouth open as much as possible during this experiment.) Does the candy appear to sparkle and glitter as you bite down on it? Stress in sugar crystals is creating an electric field! These fields are taking outer electrons from molecules, recombining them with electrons, and giving off light. What colors can you see? Does having braces on your teeth make a difference in the result?

The solar wind is always blowing. Solar storms that make sun spots also give the solar wind more energy. A stronger solar wind shifts the auroras from the Arctic to positions at lower latitudes, such as where most people in the United States live. Watch for possible auroras where you live. Do a library search of old newspapers to see if the aurora has ever been visible in your town. When? How often?

Newton's Apple is a production of KTCA Twin Cities Public Television.
Made possible by a grant from 3M.
Educational materials developed with the National Science Teachers Association.