Note: It's important to remember that the change in the length of the light wave ( ) can be calculated using this equation: Additional Note: The equation above will have a negative answer when the initial wavelength is longer (or greater in it's value) than the final length of the wave. The outcome of this calculation, whether positive or negative, tells us the direction of the star's motion. If the is positive, meaning the wave has become stretched, then the star is moving away from the observer. The opposite is true as well. If the is negative, meaning the light wave between the emitter and observer is becoming smaller and more compressed, then the star is moving towards the observer. Final Note: Numeric answers must be rounded to the nearest tenth, and can be positive or negative. Express the directional part of your answers using the words "away from" or "towards".