Doppler Effect. Redshift and blue shift

The Doppler effect is a phenomenon that occurs when there is a change in the perceived frequency of a wave due to relative motion between the source of the wave and the observer. This effect can be observed in different types of waves, such as sound and light, and plays an important role in various fields of study, from astronomy to medicine.

The Doppler effect is based on the idea that when a wave source approaches an observer, the waves are compressed, resulting in an increase in the perceived frequency. On the other hand, when the source moves away, the waves elongate, resulting in a decrease in the perceived frequency. This is because the relative motion between the source and the observer affects the wavelength of the wave.

In the case of sound, the Doppler effect can often be experienced when listening to an ambulance siren or police car rapidly approaching and then moving away. As the vehicle approaches, the sound appears to be higher pitched, with a higher frequency, and as it moves away, the sound appears to be lower pitched, with a lower frequency.

In astronomy, the Doppler effect is used to determine the motion of stars and galaxies. By observing the redshift or blueshift of the spectral lines of light emitted by these celestial objects, scientists can infer whether they are moving away from or toward the Earth, as well as determine their relative velocity.

In medicine, the Doppler effect is used in techniques such as Doppler ultrasound, which makes it possible to visualize and analyze blood flow in the human body. By using ultrasound waves, the change in the return frequency of the waves reflected by the moving red blood cells can be measured. This provides valuable information about the state and speed of blood flow in specific blood vessels.