Stephen Fry: It’s to do with the bending of light and the eye not accepting it, essentially. But it is genuinely below the horizon, physically, i.e. in other words, the Earth is turned such that it is not there. … Light from the setting sun passes through our atmosphere at a shallow angle which is gradually bent as the air density pressure increases, not dissimilar to the image of your legs when you sit in a swimming pool. The effect is to artificially raise the sun in the last few minutes of its decline. And by coincidence, the amount of bending is pretty much equal to the diameter of the sun.