At BC Place Stadium, we call this effect "The Eye Of Sauron". What's happening is that on sunny days, the rood on the stadium is pulled open like the iris of some gigantic eye. The golden evening sun penetrates the haze and smog of the city at such an angle that it looks like the shape of a massive, fiery, cycloptic unblinking eye. The assembly that pulls the guy wires is in a cylindrical pod that hangs directly in the center of the iris. It blocks the sun, making the eye look very much like it has a pupil.
This fearsome eye holds us in thrall of its gaze for nearly an hour before it melts away when the sun sets. Of course, I've goosed the effect a little using Photoshop, but not as much as you'd think. Friends of ours who sit directly in the gaze of the thing say it's incredibly dazzling. I would add stunning, or perhaps evocative.