There are two basic ways to take picutres:
We can orbit the asteroid with the camera pointing directly below the spacecraft the whole time. This is called a lattitude scan. This way, in six hours, we would see a section of the asteroid about this size, where the light gray part in the above picture is the visible asteroid.
Or, we can slew the camera up and down as we orbit. This is known as a longitude scan. In six hours, we would see this much of the asteroid -- you can see this is quite a bit more than we saw with the lattitude scans.