Angels and Hoods

I've been watching The Bible again.  The voice over is still kind of irritating, but I'm interested to see how they finish the series out.  I think I vaguely remember at one point hearing about why angels are always depicted wearing hoods, but I can't remember the reason.  This actually made me realize that I know very little about angels at all.

For a while, I think, I struggled with the idea of angels because of a book I had read when I was younger which struck me as being completely off the wall and outside of Christian beliefs.  For some reason, it always made me leery in the future about learning anymore about them.  I dont' really know how much good literature is out there about angels, but if there are some good books, I'd love to read them.  In the meantime, I'm left wondering about what the deal is with these hoods.  All the angels in The Bible are depicted with them, and I think it was mentioned in Dogma, and I know I've seen this in other movies and paintings, but I guess it's just something that never really sank it.  I think it's kind of a neat characteristic of them, though.  Another thing I've always wondered about is the "choir of angels".  I think I really need to get a journal to write down all these questions I have and start recording some answers.