Scott raised his hand with more enthusiasm than he normally would, after all; he found astronomy exciting.

"Professor I believe that Astronomy is a part of science that studies celestial objects, space, and the physical universe" he smiled.
He cautiously continued, careful of what others had said already, as to not repeat them. "Furthermore, it studies the size, motion and position of these objects"

Maybe he was wrong, but who cares? They can't penalize you for not being entirely sure.