Motion of an observer makes him measure Doppler shifted light coordinates. These Lorentz transformations relate the velocities of particles which different observers measure, and change by aberration the directions, in which incident light rays are perceived. Aberration is conformal: angles and relative sizes of small, neighbouring objects agree in aberrated pictures. Lorentz transformations determine how the energy and the momentum of a particle depend on its velocity. The conservation of energy and momentum restricts the decay of a particle and the scattering of two particles with observable consequences.