What term describes the phenomenon when a star moves towards the observer, resulting in a decrease in the wavelength of its emitted light?

The phenomenon where a star moves towards an observer, causing a decrease in the wavelength of its emitted light, is known as the blue shift. When an object in space, such as a star, approaches Earth, the light waves it emits are compressed, resulting in shorter wavelengths. This shift towards shorter wavelengths falls within the blue part of the spectrum, hence the term "blue shift."

In contrast, red shift, which is sometimes confused with blue shift, occurs when an object moves away from the observer, leading to lengthening of the wavelengths into the red part of the light spectrum. Green shift is not a recognized term in astronomical contexts, and gravity shift does not pertain to the wavelength changes associated with the movement of stars. Understanding blue shift is crucial for astronomers as it provides insights into the motion and dynamics of celestial objects in the universe.