My learnin' for today

I have always spelled the word visible.. with an a. Visable. It just sounds right, as far as how I pronounce it. I guess it makes sense, it goes with vision I suppose. I'm certain I've also spelled it visability. I don't say vis-IH-bility... I say vis-UH-bility... right? Anyway. I've always thought I had a grasp on spelling, it was always my favorite subject. Lucky me I wasn't in a Spelling Bee.. that would have been embarrassing!