Any object that's set to Global in the properties pane will not be destroyed upon changing layouts. If you want a global HUD/UI, I suggest that you create it on its own layout, and when the game starts go main menu -> UI layout -> level layout.
Make your sun and moon objects (and anything they're attached to) global as well.
In both instances, just be sure to manage them properly when you go back to the main menu or any non-game layouts. They'll still be there; easiest way is to just set them as invisible. For interactive UI elements, be sure to set their interaction conditions to include "is visible" so they're not activated when they're hidden.