The planes fly at an altitude of about 5 km. Compared to the distance to the sun and the plane (approximately 150,000,000 km), the distance to the galloping plane and the ground is negligible. For the last five kilometers the sun’s rays travel almost parallel. This is a very important detail. Remember. Let’s see why later.
Suppose a Boeing plane is 50 meters long and 5 meters wide. That is, its size is 250 square meters. Midnight – If the aircraft is ‘parked’ at the airport, it will form a 250 square meter shadow on the ground. (In the evening, however, you know that the angle of the sun’s rays is different and the shadow is larger).
Let’s take the same plane, this afternoon, take off and fly in cruising altitude. It is approximately 5 km above the ground. In the first paragraph, let’s say ‘important detail’. According to it – as the sun’s rays travel almost parallel to each other – this plane should occupy the same 250 square meters of shady ground. Also occupies.
But that shadow is not what we normally see. Why? The air molecules that encircle the center of these five km scatter the beams of light, causing the shadow to merge with the gall before it falls to the ground. That’s it. Except that the higher the plane is flying, the smaller the shadow becomes, and the less it shrinks invisibly. No matter what height it is, its shadow will take on the same size on earth. Even if these air atoms in the middle do not get in the way it looks clean to us.