I found an answer from en.wikipedia.org

Special relativity - Wikipedia

The speed of **light** in **vacuum** is the same for all **observers**, regardless of the
**motion** of the **light source** or **observer**. Contents. 1 Origins and significance; **2** ...

For more information, see Special relativity - Wikipedia

I found an answer from content.wolfram.com

The Physics of Subatomic Particles

ones are used, m, is the **rest** mass of the electron, e is its charge, Z is the ... In
1926, **two** comparatively contemporary theories of particles as **waves** grew up. ...
sion in a particular set of readings, and in most practical **situations**, **this** i s ... to
**move** in the same orbit, must now **move** in **slightly** different orbits because of thei
r.

For more information, see The Physics of Subatomic Particles

I found an answer from www.khanacademy.org

**Doppler effect** for a **moving observer** (video) | Khan Academy

What happens when just the **observer** is **moving**? ... **Doppler effect** formula for
observed frequency · **Doppler effect** formula when **source** is **moving** away ... https
://www.khanacademy.org/science/**physics**/mechanical-**waves**-and-**sound**/doppler
- ... How **do** you get the **wave velocity** if they only give you the **wave** frequency
and ...

For more information, see **Doppler effect** for a **moving observer** (video) | Khan Academy

The Doppler effect for sound waves is asymmetric, even though for the same relative motion in (i) and (ii) situations, the apparent shift in frequency is not the same. The explanation is that __sound waves need a medium for their propagation,__ and the motion of the observer relative to the medium is different in two situations. That is why Doppler's formulas for sound are different in the two cases.

The Doppler effect is symmetrical for light waves, even though the same relative movement in case (i) and (ii). the apparent shift in frequency is same. The above two cases are similar in the case of light waves travelling in vaccum since the __speed of light in vacuum is independent of the motion of the observer and the motion of the source(medium).__

However, if light travels in a medium, the two situations above are not equivalent since the speed of light in a medium depends on the refractive index of that medium.

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https://www.youtube.com/watch?v=vDvIhiCnatE