The particle-wave duality of light concerning its speed.

[Laurence Clark Crossen]

If we suppose that light in the vacuum of space moves like a particle, sharing the speed of its source (per Galileo), then its speed is C +- v.

Whether light is a particle or wave, it will slow down when it enters interstellar gas and the Earth's atmosphere.

However, we know from the Doppler effect that the star Sirius is moving 5.5 km/sec towards the Sun (or vice versa).

How can we know the relative motion from the Doppler effect unless light forms compression waves when entering the atmosphere?

Given these assumptions, light has a wave-particle duality concerning speed.