Here's why:
* Doppler Effect: This effect describes the change in frequency (and therefore wavelength) of a wave as the source of the wave and the observer move relative to each other. Imagine a siren moving towards you: the sound waves are compressed, making the pitch higher. As it moves away, the waves stretch out, lowering the pitch. Light behaves similarly.
* Stretching Wavelength: When a light source moves away from you, the waves emitted are stretched out, increasing the wavelength. Since red light has the longest wavelength in the visible spectrum, this shift towards longer wavelengths is called "redshift."
Important note: Redshift doesn't necessarily mean the object is red. It just means the wavelength has shifted towards the red end of the electromagnetic spectrum. The object could be emitting any color of light, but its wavelength will be longer than if it were stationary.
Applications:
* Astronomy: Redshift is a crucial tool in astronomy, used to determine the distance and velocity of celestial objects.
* Cosmology: Redshift provides evidence for the expansion of the universe, as distant galaxies show a redshift that increases with their distance.
