The spectrum of a distant star contains sodium lines that are offset from their normal position, as shown. What is the most likely explanation?

Question

Sodium spectra
A. The star is relatively hot.
B. The star is relatively cool.
C. The star is moving rapidly toward us.
D. The star is moving rapidly away from us.

Answer 1

The offset of sodium lines in the spectrum of a distant star is most likely due to the Doppler effect, which occurs when the source of light is moving relative to the observer.

• If the lines are shifted toward the blue end of the spectrum, it indicates that the star is moving toward us (blue shift).
• If the lines are shifted toward the red end of the spectrum, it indicates that the star is moving away from us (red shift).

Without specific information about whether the lines are blue-shifted or red-shifted, we can't definitively choose between options C and D. However, since the question refers to lines being offset, the most general answer considering common scenarios is that the star is moving rapidly toward or away from us.

If the lines are identified as being red-shifted (shifted to longer wavelengths), the most likely explanation would be:

D. The star is moving rapidly away from us.

Conversely, if they were blue-shifted, the answer would be C, but with typical interpretations of offset lines, the interpretation usually defaults to redshift unless indicated otherwise.