Question

A star is observed moving away from Earth. What can you conclude about the spectrum of that star?

The spectrum will shift to the blue.

The spectrum will shift to the red.

The spectrum will not change.

The spectrum will shift first to the blue, and then to the red.

Answer 1

The correct answer in this question is the second option. The spectrum will shift to the red. Redshift occurs when light is coming from an object that is moving farther away from the observer. This would result to longer wavelengths.

Answer 2

The spectrum will shift to the red.

Step-by-step explanation:

This phenomenon is called as 'Doppler effect'. Doppler effect occurs when a source of waves moves relative to an observer: when this happens, the wavelength of the observed wave appears shifted to the observer.

In this situation, the source of the waves is the star, which emits light (the waves). The observer is on Earth, and the star (the source of the waves) is moving away from the observer: therefore, the wavelength of the light observed by us is shifted with respect to the original wavelength of the light emitted by the star.

In particular, we have two different situations:

- when the star moves away, the wavelength increases, so it shift towards the red (which corresponds to light with longer wavelength) - this effect is called red-shift

- when the star moves towards us, the wavelenght decreases, so it shift towards the blue (which corresponds to light with shorter wavelength) - this effect is called blue-shift

In this situation, the star is moving away from us, so the correct choice is

The spectrum will shift to the red.