Light from a distant galaxy arrives with its spectral lines shifted towards longer wavelengths. What does that show?

1. Each element absorbs and emits at its own set of wavelengths, giving lines at known positions. 2. Comparing those lines with their usual positions shows how far the light has been shifted. 3. A shift to longer wavelengths is called a redshift. 4. In Doppler terms a redshift means the source is moving away from the observer. 5. A shift to shorter wavelengths would be a blueshift, and that is the one that means approach. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Chapter 6: Doppler effect_