by 
Kurdawar
ANSWERS: 2
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Lack of reference points. We cannot see motion directly, we can only see motion against reference points - usually a background, but if we are looking at an aircraft against a clear sky, the reference point is the position of our head and field of view. But if we are in a moving car, our visual system knows that the position of our head is not a valid reference point, because we are obviously moving compared to the local environment. So, if the plane is moving on a clear sky, ther is no reference to measure its motion against, so the optical system says "I give up - I cannot measure its speed". A lower level of the brain says "since I cannot measure its speed, it isn't moving".
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A really good question. Every child sees and wonders about this. People see motion as a change of angle in the visual field. That why the moon appears to go with you when driving in the car (or better, looking out the side window). The angle doesn't change much. Only the angles of things close to you change. As an adjunct idea, when a missile flys toward a target, it will hit only the thing which does not change it's angle from the view of the missile.
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