Blue shift is a phenomenon observed in light waves when an object moves closer to an observer. As the object approaches, the wavelengths of the light it emits or reflects become shorter, shifting towards the blue end of the spectrum. This effect is commonly seen in astronomy, where it helps scientists determine the movement of stars and galaxies. In contrast to red shift, which occurs when objects move away and light wavelengths stretch, blue shift indicates an object is getting closer. This principle is crucial for understanding the dynamics of the universe and the motion of celestial bodies.