What to Listen For

There are two important kinds of signals:

(click to hear)
  • Contains a single frequency.
  • Spectrum is narrow.
  • Doesn't occur in nature.
  • Sources: TV/Radio stations, cell phones
  • Broad-band
  • Contains many frequencies.
  • Spectrum is broad.
  • Occurs in nature.
  • Sources: stars, planets, nebulae

  • (click and drag to change frequency)

    So if we hear a narrow-band signal, it's either an ET, or it's a man-made signal coming from Earth.