Sorry I forgot you dont understand the topic, let me rephrase what I meant so you can understand.
Only the **speed** at which a photon moves (in a vacuum) is constant and independent of the source. The **direction** in which it moves however is relative.
Please stop repeating that light has no mass and other things you dont understand. I already provided for you the equation that is used to calculate a photons effective mass
Again it doesnt have **rest** mass, which should be obvious since it cant be at rest.