This calculation does not yield the actual speed of the object, as it fails to account for the fact that the speed of light is finite. When we measure the movement of distant objects across the sky, there is a large time delay between what we observe and what has occurred, due to the large distance the light from the distant object has to travel to reach us. The error in the above naive calculation comes from the fact that when an object has a component of velocity directed towards the Earth, as the object moves closer to the Earth that time delay becomes smaller. This means that the apparent speed as calculated above is greater than the actual speed. Correspondingly, if the object is moving away from the Earth, the above calculation underestimates the actual speed.