Reality - rays or waves, or more? Geometric rays neatly explain the shape of Rasid's shadow tunneling through mist to create the eerie Brocken Spectre. Then they fail. The contrast between sunlit and shadowed mist is beyond their accounting.
The glory centred opposite the sun is certainly past ray optics' reach. In a sense it is even beyond that of waves. 'Diffraction', the interaction between waves scattered by small fog droplets must play a role. But that is as far as it goes for there is no comfortable easily pictured way that waves or diffraction explain the glory's central brightness and multi-coloured sparkling rings.
Gustav Mie's scattering theory of 1908 directly derived without approximation from James Clerk Maxwell's 1873 equations of electrodynamics finally predicted the glory very well indeed. Run IRIS to show Mie theory's ability. Yet that could still leave us less than satisfied, it predicts but it fails to explain in terms of the ordinary world.
The sight of a glory tells of that world's strangeness.