A photon is emitted at an angle by a star (system K) and then received at an

Question:

A photon is emitted at an angle θ by a star (system K’) and then received at an angle θ on Earth (system K). The angles are measured from a line between the star and Earth. The star is receding at speed v with respect to Earth. Find the relation between θ and θ’; this effect is called the aberration of light.