A Radio Astronomer Points a Radio Telescope Through the Milky

question 119

Multiple Choice

A radio astronomer points a radio telescope through the Milky Way's disk in a direction directly away from the center of the Galaxy. If the astronomer measures the Doppler shift of the 21-cm radio line of hydrogen from interstellar clouds at several different distances from the Sun along this line of sight, what should be the result? Refer to Figure 16-8 from the text.

• A) The Doppler shift should have a constant value, regardless of distance, as a result of the Sun's speed of motion around the center of the Galaxy.
• B) The Doppler shift should be almost zero for all clouds, regardless of distance.
• C) The Doppler shift should rise to a maximum at some distance, then decrease again.
• D) The Doppler shift should be larger the farther away the cloud is.

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