While the sun near the horizon might seem to be larger than when overhead, its distance and size never changes as it moves across the sky. One hypothesis suggests that the atmosphere acts to magnify the rising sun along the horizon, but data actually suggests that the atmosphere makes the celestial body about 1.5% smaller. What we see is an illusion of the mind. The specifics behind the illusion continue to be up for debate, but make no mistake, your perceptions about the setting sun is not reality.

"Why Does the Moon Look so Much Bigger near the Horizon?" HowStuffWorks. HowStuffWorks.com, n.d. Web. 03 Feb. 2015.