From laboratory measurements,we know that a particular spectral line formed by hydrogen appears at a wavelength of 121.6 nanometers (nm).The spectrum of a particular star shows the same hydrogen line appearing at a wavelength of 121.8 nm.What can we conclude?
A)The star is moving toward us.
B)The star is moving away from us.
C)The star is getting hotter.
D)The star is getting colder.
E)The "star" actually is a planet.

Question

Quizplus · Accepted Answer

This is an example of the Doppler effect, where the wavelength of light appears shifted due to the motion of the emitting object. A shift to longer wavelengths (redshift) indicates the object is moving away, while a shift to shorter wavelengths (blueshift) indicates the object is moving towards us. In this case, the star's hydrogen line appears at a longer wavelength than the laboratory measurement, indicating that the star is moving away from us.

From Laboratory Measurements,we Know That a Particular Spectral Line Formed