Space: Doppler Effect

The Doppler Effect is the change in observed frequency and wavelength of a wave in relation to an observer moving relative to the wave source.
In the context of space and astronomy, it’s typically applied to light waves from stars or galaxies.
When a light source moves towards an observer, the wavelength shortens and the light appears bluer. This is known as blue shift.
Conversely, when a light source moves away from an observer, the wavelength lengthens and the light appears redder. This is known as red shift.
The changes in wavelength can signify the speed and direction of the object’s motion relative to the observer. This is critical to deduce the universe’s expansion rate.

The change in observed frequency can help calculate the velocity of the source relative to the observer. The formula v = c (λo - λe) / λe can be used, where:
- v is the velocity of the source.
- c is the speed of light.
- λo is the observed wavelength of light.
- λe is the emitted wavelength of light.
A positive velocity obtained represents motion away (recession), whilst negative indicates motion towards (approaching).

Edwin Hubble’s key observation of redshift in distant galaxies led to the concept of an expanding universe, underpinning the Big Bang theory.
The relationship between red shift and distance to galaxies provides evidence of the universe’s expansion and gives insight into its age.
It’s essential to note that the Doppler effect applies up to certain scales. For extremely distant galaxies receding at speeds near to light speed, the Doppler effect becomes distorted due to relativistic effects. This is governed by Einstein’s theory of relativity.
Understanding these principles allows scientists to calculate distances to other galaxies and deduce the structure and evolution of the universe.