If so it's for the navigator to use a sextant to determine position from the star
Or, on the Canadian side of the Arctic, in the Area of Compass Unreliability, the dome would be used with an astro compass to take a simple sun shot, in order to re-set the gyro compass.
Of course, bush pilots never knew about navigators: they would turn the aircraft until the sun's shadow on the glare shield behind the windshield center post was on the a/c centreline, which give the same info, in a pinch.
Question: would an overhead dome in the cockpit qualify it as a 'glass' cockpit?