https://en.wikipedia.org/wiki/Haidinger%27s_brush is a real and really cool phenomenon, but it detects light polarization, not magnetic orientation.
I was just able to see the effect for the first time using this image [1] full screen on my phone :) Brightness up, screen rotation off, hold out the phone and turn it like your steering a car. Jumped right out at me. It's always at the center of my vision, so if I look around the screen as I'm turning, it follows. The yellow always points to the longer edges of my phone. It's hard to hold it in view when not turning though.
[1] http://www.solidbackgrounds.com/images/2560x1600/2560x1600-v...