Recently, early one morning, they observed a huge Moon on the horizon. I then pondered, why is it so huge there? Refraction of light? Something else?
I googled it. It turns out that scientists do not have a definitive answer to this question. There are only a set of theories. Here are the main points on the topic.
Firstly, the Moon does not actually increase in size at the horizon. This fact is easy to check: take 2 photos / sketch the angular dimensions on paper / hold a coin at arm’s length against the Moon and look with one eye / look at the Moon through a rolled-up paper tube, etc.
The Moon definitely does not increase because of the atmosphere. On the contrary! To be precise, because of the atmosphere and refraction, the Moon decreases vertically and becomes slightly flattened.
When the Moon is at the horizon, its angular sizes actually decrease: it becomes further from the observer by a distance approximately equal to the radius of the Earth.
Visually, any objects at the horizon look bigger, for example, constellations. Our brain attributes about 1.5 times more size to the object. The shape of the horizon and the objects on it also play a role: some give more apparent enlargement, others less. Thus, one of the reasons: a simple optical illusion of comparing objects, not the atmosphere at all.
Any objects in the clear sky, if you stand up straight and tilt your head back, will seem smaller. Conversely, if you lie down horizontally and compare the Moon against a clear horizon (i.e., tilt your head back), and then while lying down look up at the sky, the effect will change. This is an effect in the brain due to the position of the head.
Less significant facts explaining the illusion: https://ru.wikipedia.org/wiki/Иллюзия_Луны
Hi, I'm Rauf Aliev. 