I've got my hand up

So we got one of those world map shower curtains. It makes bathroom time infinitely more interesting - and educational. I do have a question though. What's the difference between a "gulf" and a "bay?" I'm looking at the map, and my initial theory of one being larger than the other seems to be debunked.

Of course I could look something like this up on my own, and have my question resolved in no time. But I was one of those kids that never raised her hand in grade school so I'm making up for it now.

I'll expect responses in paragraph form.

Thank you, that is all.