Littorio shows TWO southern hemispheres on her celestial body. Judging by her eyes, Hibiki noticed this.
This is the Southern Hemisphere.It refers to the half part south of the equator for planets (including Earth) and other such celestial bodies. Here, the seasons are reversed compared to the Northern Hemisphere, and clouds and water both spiral in the opposite direction.
Due to the Coriolis effect arising from the Earth's rotation.