Longer than 1 sec shutter speed on Canon A80 "Av"-

[Inkyape]

I just got my A80, and I love it by the way, but I like to shoot pictures in low light using a tripod. I dont mind the shutter time, as the objects are still. (still lifes and night landscapes)
I know that i can use the "M" setting to adjust the aperture and time to whatever i like, up to 15 sec.
I find the "M" setting very good, but I would like to have a graph showing directly if the shot will be under - or overexposed, instead of the (-2) or whatever that shows up when the shutter is half-pressed.
Anyway-

Here's my question - Since I like to set the aperture high (8.0) to get maximum sharpness all over the picture, I'd like to use the "Av" mode, and set the aperture to 8.0 - so that the camera can choose whatever time it likes up to 15 sec. However, when I do this with a motif which is very dark, the camera sets the shutter to a "1"",showing in red (meaning underexposed) , but never more than that!
Why doesn't it shoose a longer time? Like 2 or 10 or 15 seconds?
Is there a maximum time of one second in "Av" mode??
And if so, WHY?, and must I use the "M" mode for this? That would limit the "Av" mode to "kind of bright" pictures!
Still love it though, please respond