If atmospheric refraction qualifies as an illusion then technically every sunrise is an illusion; the sun's true position is below the horizon when you see it rise even on a normal day, but atmospheric refraction causes it to appear at least one diameter higher than it otherwise would (if earth were an airless rock). Atmospheric refraction varies with factors such as temperature and altitude over the horizon, which is why the sun and moon usually look "squashed" as they rise and set; the top is refracted less than the bottom under normal conditions. When astronomical objects are that close to the horizon, changes to the amount or form of refraction due to local conditions become the most significant. Inversion layers in particular can make objects appear higher than normal, either making sunrise occur prematurely or making sunset occur late.