 The refraction of almost parallel sunlight through what is essentially a 90-degree prism accounts for the wide color separation and the purity of color.The CZA can only form when the sun is at an altitude lower than 32.2°.The CZA is brightest when the sun is at 22° above the horizon, which causes sunlight to enter and exit the crystals at the minimum deviation angle; then it is also about 22° in radius, 3° in width.