Here's why:
* The Doppler Effect: The Doppler effect describes the change in frequency (and therefore wavelength) of a wave as the source of the wave moves relative to an observer.
* Blueshift: When a source of light is moving towards an observer, the waves are compressed, causing the light to appear bluer (higher frequency, shorter wavelength).
* Redshift: Conversely, if the source is moving away from the observer, the waves are stretched, making the light appear redder (lower frequency, longer wavelength).
Important Note: While light can be blueshifted, it can't travel faster than the speed of light (approximately 299,792 km/sec). The observed shift in frequency is a consequence of the relative motion between the source and the observer.
