It’s an aspect of the nature of light, because it travels uniformly in every direction from the point of its source, that upon encountering any evenly distributed scattering of objects, it produces the illusion of an enclosing sphere. This is perhaps most familiar in the globe that surrounds headlights seen through a rain-fogged window or a distant streetlamp observed through heavily falling snow.
Early fall reminds me of a slightly different manifestation of this same effect. Overcast light, diffused through deciduous forest canopy, strikes thinning, yellow-green leaves in such a way as to transform trunks and branches into arching pillars and a gold-carpted trail through woodland to a corbeled, green-golden cathedral vault, like the grand passage leading through the Emerald City to the doors of the Wizard’s audience chamber.