A star shifting to the red spectrum is moving farther away from us. This is due to the Doppler effect, which is the same phenomenon that causes the pitch of a siren to change as it moves towards or away from you.

Here's how it works:

* Light waves: Stars emit light, which travels in waves.

* Redshift: When a star moves away from us, the light waves it emits get stretched out. This stretching shifts the light towards the red end of the electromagnetic spectrum.

* Blueshift: Conversely, if a star is moving towards us, the light waves get compressed, shifting the light towards the blue end of the spectrum.

This redshift/blueshift phenomenon is a key tool for astronomers. It allows them to determine the movement of stars and galaxies in the universe and has been instrumental in understanding the expansion of the universe.