Silas Laycock at The Conversation:
People mainly notice the Moon looking bigger and closer when it is full and near the horizon. This is because your mind judges how big or small an object like the Moon is by comparing it with other, familiar things.
Imagine you are standing outside close to your house. Your house will look big, and if the Moon rises next to it, the Moon will look normal. If you look at a house from far away, though, the house looks very small.
The illusion comes from the fact that the Moon is so far away that no matter where you are on Earth, the Moon always looks the same size. It is actually the things your mind compares the Moon with – a house, a mountain or anything else – that look bigger or smaller depending on how far away from them you are. So when the Moon rises next to a distant house or a faraway mountain, the Moon looks enormous.