A yellow or orange ring around the moon is typically caused by the presence of ice crystals in the atmosphere. These ice crystals act as tiny prisms, refracting and scattering the moonlight, resulting in the appearance of a colored ring. This phenomenon is often observed during cold weather conditions when cirrostratus clouds composed of ice crystals are present.

Ice crystals in the atmosphere can have different shapes, including hexagonal plates, columns, and dendrites. As moonlight passes through these crystals, it undergoes refraction and diffraction. The colors produced depend on the size and shape of the ice crystals, as well as the angle at which the light is observed. The yellow or orange coloration is usually attributed to a combination of these factors.

In general, the thickness and density of the ice crystal layer influence the intensity and prominence of the colored ring. Thicker layers of ice crystals can produce more vivid and colorful rings, while thinner layers may result in a faint or barely noticeable halo. It's worth noting that other factors such as atmospheric conditions, pollution, and the observer's perspective can also affect the appearance and visibility of the moon halo.