The Norton Asteroid Belt existed within the Aquilaean system, positioned in the space between Aquilae and the Forbidden Systems.
Luke Skywalker, along with Annikin Starkiller, Leia, Artoo, Threepio, Biggs and Windy (contained in microcases), fled from Gordon by commandeering an Imperial starship; they then navigated into the Norton Asteroid Belt, hoping to evade the pursuing Imperial hunter destroyers.
Despite successfully eliminating a number of these pursuers, their starship sustained significant damage, forcing them to abandon ship over the planet Yavin.
Evidently, Norton Three was among the many asteroids located there.
The asteroid belt sequences served as inspiration for the events that unfolded in the Hoth system belt during Episode V.