# What is the Doppler Effect and How Does it Affect Space Explorations?

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Have you heard of the Doppler Effect? It affects waves like sound and light and shapes one of the most fundamental elements in space explorations. Find out about that in this article.

#### The Doppler Effect

Imagine that you are hearing a plane taking off from a runway. The sound frequency will gradually become higher when it gets closer to you, even though the engine throttle is the same. However, the frequency will decrease when it gets farther away from you, and the sound pitch will lower. This effect is known as the Doppler Effect, where waves, including sound or light, make the wavelength smaller when the object in question moves closer and expands the observed wavelength when that object is moving farther away.

What causes this effect? You have to visualize it, at least in your mind. When the object is traveling, it emits waves more densely than usual in one direction because of the object’s velocity. The wave must have traveled a certain distance with each wavelength, but the next wavelength will be emitted in that range, causing them to be denser. As a corollary, the frequency will decrease in the other direction where the object is getting farther and farther.

#### How Does it Affect Space Explorations?

While our previous examples use sound, the Doppler Effect is an irreplaceable element in space exploration. This is because the effect also applies to light. When an object is moving away from us, the frequency of the light will decrease, meaning its wavelength will increase. This is called redshift. On the contrary, if it is moving toward the observer, the wavelength will decrease due to the increase in frequency, causing blueshift.

The Big Bang theory, the most widely-accepted theory of the birth of the Universe, is based on an observation related to the Doppler Effect. The theory is proposed when astronomers observed that almost all galaxies are exhibiting redshift, and the further the galaxy is from our Milky Way Galaxy, the stronger the redshift. A strong redshift means that the object is moving away from us quickly, while a weaker one means it’s moving away slowly. This implies that the Universe is enlarging itself, leading to the theory that the Universe started as an infinitely small point before inflating. It is also known as the Big Bang theory.

Today, redshift is used to measure the distance between us and distant galaxies. Because the Universe is expanding, the more intense the redshift, the faster the galaxy is moving away from us, and the further it is from the observer.

#### Conclusion

In this short article, we briefly mentioned the Doppler Effect and its implications on space explorations. If you want to learn more about this intriguing physical phenomenon, please visit the webpages in the references below.

#### References and Credits

1. (n.d.). The Doppler Effect. Retrieved April 5, 2022, from https://www.physicsclassroom.com/class/waves/Lesson-3/The-Doppler-Effect
2. (n.d.). What is the Doppler effect? Retrieved April 5, 2022, from https://www.qrg.northwestern.edu/projects/vss/docs/communications/3-what-is-the-doppler-effect.html