Thing about halos that is weird to me is that I always thought of them as an artistic representation of holiness and not a physical thing; we're drawing light around this guy's head to represent he's holy. I never really saw them as an actual ring or circle that you could physically interact with. I imagine that if I had a vision of someone holy, I would imagine them as bathed or draped in light, or something that seems so holy that it trascends a mere physical presence. And so I always thought halo is a way to represent that; you can't literally tell this person is holy, so you have to symbolize it a bit. It's not something you can touch.
But then again, it does seem that in many cultural representations, haloes are tangible things. It's even strange to think they include it in perspective, or with different details and such, not as a symbol, but as an actual physical phenomenon. What's interesting is that it is way older than Christianity, and it is a representation found in many Old World cultures.
