Dopplervaikutuksen

Dopplervaikutus, named after Austrian physicist Christian Doppler, describes the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. This phenomenon is commonly observed with sound waves and light waves.

When a sound source, such as a siren on an ambulance, moves towards an observer, the sound waves are compressed, resulting in a higher perceived frequency, meaning a higher pitch. Conversely, as the source moves away, the waves are stretched, leading to a lower perceived frequency, or a lower pitch. The same principle applies to light. If a celestial object is moving towards Earth, its emitted light will be shifted towards shorter wavelengths (blueshift). If it is moving away, the light will be shifted towards longer wavelengths (redshift).

The magnitude of the Doppler shift is directly proportional to the relative velocity between the source and the observer. This effect has numerous practical applications. In astronomy, Doppler shifts are used to determine the radial velocity of stars and galaxies, helping scientists understand the expansion of the universe and the motion of celestial bodies. In medicine, Doppler ultrasound utilizes the Doppler effect to measure blood flow by detecting the frequency shift of sound waves reflected off moving red blood cells. Radar systems also employ the Doppler effect to measure the speed of objects like vehicles.