The phenomenon where the sun appears on the horizon about two minutes before the actual sunrise is primarily due to atmospheric refraction. 

As sunlight passes through the Earth's atmosphere, it bends or refracts because of the varying densities of air layers. This bending causes the light rays from the sun to reach an observer's eyes even when the sun is geometrically below the horizon. 

This effect can make it seem as though the sun has risen before it truly has, resulting in a visual perception of sunrise occurring a couple of minutes earlier than the actual event.