Presenting the aberration of light effect we consider that two observers at rest in I and I' in the standard configuration equipped with laser guns start to emit light when they are instantly located at the same point in space. The problem is to find out a relationsship between the directions along which the same ray propagates when detected from the two involved frames. Presenting the Doppler we consider the the same two observers mentioned above. What we haveto compare are the period at which say observer from I emits two successive wave crests (signals) from the same point in space the moving observer receiving them being located at two different points in space That is an essential difference between the two effects. Using the invariance of the phase of a plane wave many textbooks derive a formula that acounts for the Doppler and as a byproduct the formula that accounts for the aberration. How could the two formulas be physically compatible? Thanks for your answers.