The Reason Commercial Planes May Appear To Hover In Mid-Air, Even Though They Can't

Late in 2023, a video shared on Reddit that captured a passenger plane flying over San Francisco went viral because it appeared to be levitating mid-air. While some fighter jets can hover in place, there aren't any commercial planes with the technology to do so. What you see in the video is an optical illusion that has more to do with the concept of reference points and motion than any secret hover mode.

So, why does the plane appear frozen in place? It's because of a concept known as the Parallax Effect. Imagine you are sitting in a car and looking through its window. Objects that are closer to you appear to move faster, while those far from you appear to move slower. In reality, the object further away could be moving much faster, but due to the distance and relative pace of its movement as seen by our eyes, it appears to move slowly.

Now, imagine you are sitting in a car that is moving at the same speed as another car in the adjacent lane on a long straight road. If you focus solely on a part of the other car, it would appear still to your eyes, because there is no relative motion happening with respect to your own motion on a straight road. It's only when you look at the changing background that you realize the other car is actually moving. The background here serves as a reference point to make sense of whether an object is moving or not.

Jason Steffen, who has served on NASA's Kepler mission and is currently a professor at the University of Nevada, explained to Travel & Leisure that the position of objects relative to the background objects plays a key role in how we perceive their position. Steffen described the parallax effect, saying, "If you are moving as you film, you will see the airplane's position relative to the background. If the motion of the video camera keeps the airplane in line with a background object, you won't see the airplane move across the field of view."

In the context of airplanes appearing to hover in place like a helicopter, the effect is most pronounced when the sky is clear and you see the plane against a clean blue backdrop. In the viral video, the plane appeared suspended mid-flight with a blue body of water as its background. If you're an onlooker in another airplane, you will most likely notice this effect if your plane moves at the same speed or faster as the one you're watching. From your perspective, the other plane would appear to be still in the air.

Once again, the nature of a reference background is important. If it's plain or flat, there is nothing for your brain to use as a reference point. In such scenarios, where the brain can't do a proper depth estimation, the moving object appears motionless. It's an aspect of physics that may change your view of the universe.