[JediKooter]

I'm thinking it may just be the moon light. Much like if you have a large body of water and there's a full moon. Regardless of where you are located, speed you are going and what altitude you are, there will always be a very 'focused' beam of moonlight on that body of water and it will appear to be moving with you.

Let me see if I can find a picture of what I'm talking about...be right back


Edit: Here we go. The moonlight is shinning everywhere, but, from our perspective, it looks like it's focused in a narrow band. If there was a lot of moisture in the air, I think that would also help with the effect.