Before the queen can capture the king, the queen must first have put the king in check. And it can only do this when it has crossed the borderline. White queen (here blue) can only do this on ranks 5-7, black queen (here red) analogously on ranks 1-3.
@Fergus
Before the queen can capture the king, the queen must first have put the king in check. And it can only do this when it has crossed the borderline. White queen (here blue) can only do this on ranks 5-7, black queen (here red) analogously on ranks 1-3.