A white, vertically elongated sport of light that arises through reflection by horizontal faces of ice crystals.
This optical phenomenon is known as an undersun. It can be seen within clouds or haze when observed from above. Numerous tiny ice crystals suspend in the atmosphere and the Sun’s light is reflected off of them.
As a large mirror, the region of ice crystals create a virtual image of the sun. One can see it within clouds or haze. The effect belongs to the family of halos.