* The Doppler Effect: The Doppler effect is a phenomenon where the frequency of a wave (like light) changes depending on whether the source of the wave is moving towards or away from the observer. Think of a siren: as it approaches, the sound waves are compressed, making the pitch higher. As it moves away, the waves are stretched, lowering the pitch.
* Light as a Wave: Light behaves as both a wave and a particle. The color of light corresponds to its frequency (or wavelength).
* Redshift: When a star is moving away from us, the light waves it emits are stretched. This causes the wavelengths to become longer, which shifts the light towards the red end of the spectrum.
* Blueshift: Conversely, if a star is moving towards us, the light waves are compressed, making the wavelengths shorter and shifting the light towards the blue end of the spectrum.
In summary, redshift in a star's spectral lines indicates that the star is moving away from us, and the amount of redshift is proportional to the speed of the star's recession.
This phenomenon is crucial for understanding the expansion of the universe. Redshift is observed in the light from distant galaxies, which tells us that they are moving away from us and that the universe is expanding.
