How to pronounce “ommatidium” in English

Their eye is a whole sort of hemisphere of little tubes looking outwards, and so you can maintain a fixed angle to something like a star or the moon by keeping the moon inone ommatidium. If you do that, because rays from the moon come from optical infinity, they’re parallel, and so if you keep of the moon in one ommatidium you will fly in a straight line.It might be say 30 degrees; keep the moon at 30 degrees to your right.