Parts of Victoria, Australia, experienced an unusual visual phenomenon over the weekend, as iridescent clouds, often called rainbow clouds, appeared in the sky. Onlookers in Melbourne suburbs such as Mount Waverley and Caroline Springs captured photographs of the spectacle.
Sarah Scully, a senior meteorologist at the Bureau of Meteorology, stated that while iridescent clouds are not uncommon in Australia, they are rarely photographed because they are fleeting. These clouds typically form from cirrus clouds, which were present over Victoria, and are composed of ice crystals found in the higher levels of the troposphere.
The rainbow appearance results from sunlight diffracting, or bending, around ice crystals within the clouds. This phenomenon often occurs in newly formed clouds where the ice crystals are of a uniform size. Iridescent clouds differ from rainbows, which involve both the refraction and reflection of sunlight, and are also distinct from sun dogs, another optical phenomenon caused by water crystals at lower atmospheric levels.