When a star or galaxy moves quickly towards an observer, the light it emits will appear blueshifted.

Here's why:

* Doppler Effect: The Doppler effect is a phenomenon that affects waves (like light) when the source of the wave is moving relative to the observer.

* Blueshift: As the source moves towards the observer, the wavelengths of the light waves are compressed, making them appear shorter. Shorter wavelengths correspond to the blue end of the visible light spectrum, hence the term "blueshift."

Important Note: The opposite is true for objects moving away from us. Their light will appear redshifted because the wavelengths are stretched out.