Why does the rising sun appear bigger

Why does the sun appear bigger at sunrise and sunset?

The previous answer is not in itself wrong, it only explains one distortion the body on the celestial sphere, not the effect you described. Processed : Refraction does not reduce the size of objects on the horizon, but it is not the reason for the perceived size.

What you mean is often referred to as the moon illusion and there are several perceptual effects in the game. It is important to understand that our brain is only able to determine distance, that is, to perceive three dimensions, two in a certain and very limited area. Everything that happens in the celestial sphere has no depth for us at all: the brain has no information at all about the distances between the sky and has to fill in the gaps. This creates some really interesting phenomena.

So the most plausible explanations are:

  1. Apparent Distance: When clouds are viewed at shallow angles in the sky, they appear noticeably smaller than directly above them because they are of course further away. The real, measurable angle size is smaller. The moon or the sun, on the other hand do not appear noticeably smaller as their actual distance does not change significantly as they move towards the horizon. But the brain would expect them to be smaller, similar to the clouds or a plane, and therefore perceive them to be larger than they "should" be.

  2. Relative size: Since the sun is only surrounded by sky above, there is nothing like it. On the horizon there are actually things to compare size to, all of which are smaller, and so the brain corrects that.