ORIGINAL: touch and go

The rules of the sea, and the air, are that if two vessels, or aircraft, are on a collision course, such as converging at a right angle to each other, the vessel/aircraft on the right has the right of way. Thus, by putting the green light on the right side of a vessel or aircraft and the red light on the left side, as the two converge the captain of the craft on the right side will see a green light on the other craft indicating that he has the right of way and the captain on the left side will see a red light indicating that he does not have the right of way. That's why the lights are set up as they are.