Look up at the dark clear moonless night-time sky. What do we see? Points of light arranged against a deep dark background. I propose that in the points of light we see physical substance, matter, and in the darkness we are looking into the encompassing ethereal realm.
There are certain fundamental processes in the universe, one of which is expansion and contraction. Goethe observed this in plants and in crystallisation out of solution we see a contraction of a substance into its solid state.
Likewise the points of light we see in the night sky are processes of matter condensing out of the surrounding ethereal space. The ethereal creates a void in which matter forms and cosmic space which is void of matter is actually filled with etheric activity.
The processes of expansion and contraction are taking place at all levels, as above, so below. Our physical eyes allow us to see the stars and other heavenly bodies but it takes more than physical senses to see the etheric.