I have a starship moving at a speed v, which is larger than .5c, away from Earth in the x direction. A blast of its phaser banks (assume highly focused light) travels at an angle (phi)'. From this I need to prove that an astronomer who observes the phaser blast moves at a speed of c, the speed of light. I have it worked out that the angular velocity of the phaser blast from the starship in the x direction is v'sub(x) = c * cos ((phi)') and in the y direction is v'sub(y) = c * sin((phi)'). Any help would be appreciated!