Suppose a rocket is moving away from earth at 0.5c. The rocket is moving towards a beam of light. There are two clocks on the rocket placed 1m apart. Each clock stops ticking when the beam of light hits it. The speed of light is then calculated as d/t = 1/(t1-t2). What effects occur for the calculation to yield c instead of 1.5c , and what is going on on a more intuitive level?