When a star moves towards Earth, the light it emits shifts towards the blue end of the spectrum. This phenomenon is called blueshift.

Here's why:

* The Doppler Effect: This effect describes the change in frequency of a wave (like light) due to the relative motion of the source and observer. When the source moves towards the observer, the waves are compressed, resulting in a higher frequency.

* Light and Frequency: The color of light is directly related to its frequency. Higher frequencies correspond to bluer colors, and lower frequencies correspond to redder colors.

Therefore, as a star approaches Earth, the frequency of its emitted light increases, causing it to appear slightly bluer.