It is possible that you’re unfamiliar with what a sun pillar happens to be. You’re certainly not alone there. If you are not aware, sun pillars are a rare optical phenomenon that is actually caused by the reflection of sunlight off ice crystals in the air. If you do see one, it usually pops up more often during sunset/sunrise periods as this is the time when the aforementioned reflection is most common. Ice crystals in the air usually will come as a result of snow. Of course, snow only occurs when temperatures in the clouds are below the freezing point. Water vapor in the atmosphere condenses directly into ice without needing to go through the liquid stage. Thus, when sun pillars do happen, they’ll occur only due to this situation. However, they can happen over cooler mountain areas too while we can see it below without ice crystals.