In 1842, physicist and mathematician Christian Dopplerfound that if the sound source and the observer move relative to each other, the frequency of the sound perceived by the observer does not coincide with the frequency of the sound source. Today we call this phenomenon the "Doppler effect" and it is with its help that astronomers search for exoplanets - worlds that revolve around other stars outside our solar system. Of the 473 exoplanets known to date, 442 have been detected using the Doppler effect, which describes changes in the frequency of any kind of sound or light wave produced by a moving source relative to the observer. The phenomenon, discovered by an Austrian scientist in the 19th century, is an integral part of modern theories about the origin of our Universe and is used in weather forecasting, studying the motion of stars, and also in diagnosing cardiovascular diseases.
What is the Doppler effect?
Imagine a puddle in the center of which sitshappy beetle. Every time he shakes his paws, he creates obstacles that move through the water. If these disturbances arise at some point, they will propagate from this point in all directions. Since each disturbance moves in the same environment, they will all move in all directions at the same speed.
The pattern created by the beetle's paws will bebe a series of circles reaching the edges of the puddle at the same frequency. The observer at point A (left edge of the puddle) will see disturbances hitting the edge of the puddle with the same frequency as the observer at point B (right edge of the puddle). In fact, the frequency with which the circles reach the edge of the puddle will be the same as the frequency with which the beetle wiggles its legs, we define it as two disturbances per second.
Now suppose the beetle swims towards the observerB, producing disturbances with the same frequency. Since the insect moves to the right, each disturbance arises closer to the observer B and further from the observer A and, accordingly, reaches the observer B faster. In this case, it will seem to the observer B that the frequency of arrival of disturbances is higher than the frequency with which these disturbances arise; observer A, on the contrary, will think that the frequency of disturbances is lower than it actually is. This example hopefully illustrates the Doppler effect well.
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If not, then we note that the Doppler effect can beobserve for any type of wave - water wave, sound wave, light wave, and so on. Imagine that a police car is moving towards you. When a car approaches you with the siren on, the siren sound becomes louder but becomes quieter as the car passes by. This is another example of the Doppler effect - a pronounced shift in the frequency of a sound wave produced by a moving source.
How does the Doppler effect work?
The Doppler effect is of great interest forastronomers who use information about the frequency shift of electromagnetic waves produced by moving stars in our galaxy and beyond. In fact, the researchers' speculation that our universe is expanding with acceleration is based in part on observations of electromagnetic waves emitted by stars in distant galaxies. It is also possible to determine specific information about stars within galaxies using the Doppler effect.
Modern telescopes enable astronomersstudy stars in distant galaxies. Typically, they look for light sources that emit electromagnetic waves. Astronomers can observe the Doppler effect when a star revolves around its own center of mass and moves either towards the Earth or away from it. These shifts in wavelength can be seen as subtle changes in the spectrum of a star - a rainbow of colors emitted by light.
As a star moves towards us, its wavelengths are compressed, and the spectrum becomes bluish. When a star moves away from us, its spectrum glows red.
To watch the red and blue glowastronomers use a spectrograph, a high-resolution prismatic instrument that separates incoming light waves into different colors. Each star's outer layer contains atoms that absorb light at specific wavelengths, and this absorption appears as dark lines in different colors of the star's spectrum. Researchers use the shifts in these lines as handy markers for measuring the magnitude of the Doppler effect.
See also: The Mandela Effect - Why Do People Remember What Didn't Happen?
It should be noted that the Doppler effect is usednot only in astronomy. By sending radar beams into the atmosphere and studying changes in the wavelengths of the returning beams, meteorologists are looking for water in the atmosphere. The Doppler effect is also used in medicine with echocardiograms, which send ultrasound beams through the body to measure changes in blood flow to make sure the heart valve is working properly, or to diagnose cardiovascular disease.