Glass windows

Here's something. When I read of bases on the Moon, there is usually
talk of burying it under five metres of soil. This always puzzled me,
as two seems to be considered enough for an O'Neill habitat, when the
rays can come at you from any direction, but on the moon, where you
have multiple terratons of solid Moon shilding you from all but about
45 of sky, it needs to be more?