I live about 20 miles from the local airport, directly under a common flight path.  Because of this I constantly have airplanes fly over my house as they are coming in to land.  One thing that I have observed is that just after sunset, but before dark, if I look up in the sky at one of these planes, I can see them clearly as they are lit from the sun from below.  This fact is something that has been known since the dawn of military aviation as even the most stealthy of aircraft is visible clearly from the ground after the sun has set on the ground below but before the sun has set on the airplane.  This makes perfect sense from a RE perspective as the sun would actually be below the airplane at this point.  How does this phenomenon work from a FE perspective?  From what I understand the sun is a constant 3000 miles above the surface of the plane of the earth. How then does a flying aircraft become lit form underneath? Please explain.