At an Astronomical Conference, an Astronomer Gives a Report on a Star

question 27

Multiple Choice

At an astronomical conference, an astronomer gives a report on a star that interests astronomers because of hints that it may have a planet around it. In his report the astronomer gives the average speed with which this star is moving away from the Sun. How did the astronomer measure this speed?

• A) by seeing how the luminosity of the star has been decreasing as it moves farther and farther away
• B) by seeing the whole star become much redder than it used to be
• C) by measuring the diameter of the star (which is easy to do) and noticing that it is getting smaller and smaller
• D) by looking at the Doppler shift in the lines of the star's spectrum
• E) the astronomer must be making up stories to impress his colleagues; there is no way to measure the speed with which stars move away or toward us.

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