A parhelion, or "sun dog", is the bright, often colourful spot of light that appears beside the sun when sunlight passes through ice crystals in the air. It is one of a family of sights made by ice: rings around the sun, glowing arcs, crescents, pillars of light.

Parhelion is a simulation of that family. Millions of rays of light are fired through falling ice crystals, and every token is the sky that results: a high sun or a low one, pale rings or arcs edged with rainbow colour, clear air or haze.

None of the sky is drawn. I wrote the rules for the ice and the light, then looked at what appeared. The ring around the sun, for example, is not in the code: a six-sided ice crystal cannot bend light by less than about 22 degrees, so the light gathers in a ring at that distance and the sky inside it stays dark. The colours of the arcs are not chosen either. Each colour of light bends by a slightly different amount, which is where the rainbow edges come from.

Your token's hash sets the weather: the height of the sun, the shape and tilt of the ice, the air, the ground and where the camera points. The same hash always makes the same sky, at any size.

Parhelion asks how much of a picture can be left to physics. Every ring, arc and pillar is the ice's answer.

 

For the curious: a 60° ice prism cannot bend yellow light by less than 21.84° (red a little less, violet a little more), and the 46° halo comes from the 90° angle between a side face and an end face.