According to the principles of special relativity, the speed of light in a vacuum is always observed to be the same (approximately 299,792 kilometers per second or 186,282 miles per second) for all observers, regardless of their relative motion. This is known as the postulate of the constancy of the speed of light.
So, if a ray of light is emitted from a rocket ship moving at a speed v relative to Earth, the observed speed of light on Earth will still be measured as the same constant speed of light. This means that an observer on Earth will measure the speed of light emitted from the moving rocket ship to be the same as if it were emitted from a stationary object.
The constancy of the speed of light is one of the fundamental principles of special relativity and has been experimentally confirmed many times. It leads to various counterintuitive effects, such as time dilation and length contraction, which arise from the relative motion of observers and the constant speed of light.