Chapter 1: Problem 6

Describe how the Doppler effect works. If the light you see from a distant galaxy has undergone a blue shift, is the galaxy traveling toward or away from you? (C)

Short Answer

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The Doppler effect occurs when a wave, such as light, experiences a change in frequency and wavelength due to the relative motion between the source and the observer. When the source is moving towards the observer, the observed frequency increases and the wavelength decreases (blue shift); when the source is moving away from the observer, the observed frequency decreases and the wavelength increases (red shift). If the light from a distant galaxy has undergone a blue shift, it indicates that the observed frequency of the light has increased and the galaxy is emitting light with a shorter wavelength. Therefore, the galaxy is traveling towards the observer.

Step by step solution

Understanding the Doppler effect

The Doppler effect occurs when a wave (such as sound or light) is emitted from a source that is moving relative to an observer. The observed frequency (and consequently, wavelength) of the wave changes depending on whether the source is moving towards or away from the observer. When the source is moving towards the observer, the observed frequency increases and the wavelength decreases; when the source is moving away from the observer, the observed frequency decreases and the wavelength increases.

Applying the Doppler effect to light

In the case of light, the Doppler effect can cause the observed color of the light to change, because color is determined by the frequency (or wavelength) of the light wave. When a light source is moving towards an observer, its observed frequency increases, and this causes a shift towards the blue end of the spectrum - this is known as the blue shift. Conversely, when a light source is moving away from an observer, its observed frequency decreases, and this causes a shift towards the red end of the spectrum - this is known as the red shift.

Determining the direction of motion for a blue-shifted galaxy

In the given exercise, the light observed from a distant galaxy has undergone a blue shift. This means that the observed frequency of the light has increased, and the galaxy is emitting light with a shorter wavelength. Based on our understanding of the Doppler effect, this indicates that the galaxy is moving towards the observer. In conclusion, if the light from a distant galaxy has undergone a blue shift, the galaxy is traveling towards the observer.

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Describe how the Doppler effect works. If the light you see from a distant galaxy has undergone a blue shift, is the galaxy traveling toward or away from you? (C)

Short Answer

Step by step solution

Understanding the Doppler effect

Applying the Doppler effect to light

Determining the direction of motion for a blue-shifted galaxy

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