Down sun, up moon.
Supposing this to be true (I have no idea for the moon bit, though I certainly agree for the sun bit), why is it of any practical use to know it when flying? You're not going to choose a destination based on the way the moon is shining. So once you get up there, whatever it is, it is. If you notice that you can make out ground features better on one side of the aircraft than the other, and this is useful, good for you. If you're flying at night you're hopefully not relying on pilotage for navigation anyway. This seems like it could have been a useful thing to know ahead of time in about 1920, before there was anything BUT pilotage.
The FAA written tests generally seem to be stuck in aviation as it was about 30 years ago (complicated questions about NDB navigation, for example). I guess the CAA hasn't quite got that far yet.