I’ve noticed while traveling out of Chicago on the L (the elevated train line) that the Willis Sears Tower appears as though it’s shooting upward out of the surrounding skyline. It’s pretty striking when you first see it. For a moment it honestly looks like the Tower is growing taller. Today I learned from the fantastic Futility Closet that this effect is called the Vista paradox.

You can see the effect from the rear car of north bound Brown or Purple line trains as you’re approaching the Chicago stop. The Tower appears to rise up behind the Merchandise Mart.

A gif of the vista effect as seen from the Purple line

The effect occurs because the visual angle between the Tower and the the closer buildings rapidly increases as you move away.

A sketch of the change in visual angle as you move away from the Tower

Incidentally, when the train stops after I’ve been looking out the back for a while, I also experience a vection illusion (feeling of self motion) where I continue to perceive the tracks as moving away from me even though the train is still.