Astronomers initially had difficulty identifying the emission lines in quasar spectra at optical wavelengths because:
A)the lines are created by elements that do not exist on Earth.
B)no one expected violet and ultraviolet spectral lines to be shifted so far toward the red.
C)quasars are receding from us at extremely high speeds, and this smears out the emission lines, making them hard to measure.
D)they were emission lines from ionized atoms that had not been seen before.

Question

Quizplus · Accepted Answer

The spectral lines in quasar spectra are shifted toward the red due to the Doppler effect caused by their high speed of recession. This redshift was not initially anticipated, and as a result, astronomers had difficulty identifying the emission lines at optical wavelengths.

Astronomers Initially Had Difficulty Identifying the Emission Lines in Quasar