* Decreasing Wavelength: When the wavelength of light emitted from an object decreases, it shifts towards the blue end of the visible light spectrum.
* Doppler Effect: This phenomenon is known as the Doppler effect. Imagine a siren approaching you. The sound waves get compressed, leading to a higher pitch (shorter wavelength). As the siren moves away, the sound waves stretch, leading to a lower pitch (longer wavelength).
* Motion Relative to Earth: The shift in wavelength is caused by the object's motion *relative to Earth*. If an object is moving towards Earth, the light waves are compressed, resulting in a shorter wavelength (blue shift). If the object is moving away from Earth, the light waves are stretched, resulting in a longer wavelength (red shift).
In summary:
* Blue shift (shorter wavelength) means the object is moving towards Earth.
* Red shift (longer wavelength) means the object is moving away from Earth.
