The NASA SCIence Files™
Signals From Space

Purpose: To understand how astronomers use radio waves to search for intelligent extraterrestrial life

Materials

Background

Astronomers have concluded that the most efficient way of making contact with an intelligent civilization orbiting another star is to use radio waves. Light waves would not be practical because each civilization’s planet orbits a huge source of light, its star. Sending out a light wave would be like shining a flashlight from the Sun. Stars, on the other hand, have very few radio waves, so the competition for attention is much less than light. Radio waves also penetrate the dust of space and the atmosphere of planets more efficiently than other forms of radiation. However, there are many natural processes in the universe that produce radio waves. If we could translate those naturally produced radio waves into sound, they would sound like static we hear on a radio. In the search for intelligent life, astronomers must distinguish between a “signal” (possible message) from the “noise” (static).

Teacher Prep

Locate two similar radios that can receive AM broadcasts and set them up side by side in the classroom. Try to move the desks or chairs an equal distance from the two radios. Tune one radio to static and the other to a station broadcasting someone talking. Discuss the background information to make sure that the students understand why radio waves are used instead of light waves. Before you begin the activity, explain that you are using two radios to demonstrate how static can interfere with reception. Turn up the radio with the static as loud as the class can tolerate it. Note the volume level. Turn up the volume on the other radio (with person talking) and ask students to signal when they can hear the signal against the static. Note the volume level. Have them signal a second time when they can understand what the person is saying. Note the volume level.

Procedure

Part I:

  1. Discuss radio waves and why they are used to search for intelligent extraterrestrial life.
  2. Pay close attention as your teacher adjusts the volume of the radios. In your science journal, record the volume level of the static after it reaches its highest tolerable level.
  3. Record the volume level when you can hear the other signal.
  4. Record the volume level when you can understand what the person is saying.
  5. Compare the volume level of the static to the volume level when you first heard the signal.
  6. Compare the volume level of the static to the volume level when you first understood what the person on the radio was saying.

Part II:

Even though there was a lot of static, you eventually heard the speaker and even understood what he/she said. In radio astronomy, astronomers are able to “understand” messages, even the ones that have a lot of static. If you were to put radio waves on television, they would look like a lot of dots. A computer puts a dot at each frequency where it detected some radio waves. If there are a lot of radio waves, the dot will be larger. However, the computer is not able to tell if the signal is natural static or an intelligent signal. If it is a real signal, it would remain “on” as the computer did further scans. If it is static, it would go on and off randomly. An intelligent signal would be a dot pattern that persists from scan to scan. Now you are ready to find the signals!

  1. Using scissors, carefully cut apart the Radio Data Strips.
  2. Place the strips in any order on the Radio Data Grid but be sure that the ends of the strips (with the number 88) are exactly lined up at the left edge and that the number 108 (on the right edge) is just like the first strip shown on the grid.
  3. Glue or tape the strips into place.
  4. Lay a ruler vertically across the Radio Data Grid.
  5. Starting at the left edge (88), slowly move the ruler to the left. Look for any areas where there are dots in every strip.
  6. If you find such an area, mark it by using the edge of the ruler to draw a line through all the dots. Continue to move along the grid and look for all signals.

Conclusion

  1. When riding in a car listening to the radio, there will often be static. What might be some reasons for the static?
  2. What are some sources that would interfere with the radio waves collected by astronomers?
  3. Would you like to someday look for intelligent extraterrestrial life? Why or Why not?