A striking display of rainbow-coloured clouds has appeared over parts of Victoria, giving residents a rare opportunity to photograph an atmospheric phenomenon known as cloud iridescence.
The colourful formations were spotted over Melbourne during the weekend, including in the suburbs of Mount Waverley and Caroline Springs. While meteorologists say iridescent clouds are not particularly uncommon in Australia, their brief appearance means they are rarely captured clearly in photographs.
What Caused Victoria’s Rainbow-Coloured Clouds?
Sarah Scully, a senior meteorologist at the Bureau of Meteorology (BoM), said the phenomenon can easily pass unnoticed because of how quickly the conditions responsible for it can change.
“People don’t often notice them, as they’re really fleeting,” she said.
The colourful clouds observed over Victoria are associated with the interaction between sunlight and tiny ice crystals suspended high in the atmosphere.
Iridescence commonly develops in cirrus clouds, which were present over Victoria during the weekend. Cirrus clouds form at high altitudes in the troposphere — the lowest major layer of Earth’s atmosphere and the region where most weather occurs.
At those heights, temperatures are sufficiently cold for clouds to contain ice crystals rather than only liquid water droplets.
Sunlight and Ice Crystals Create the Colourful Effect
The rainbow-like appearance is produced through diffraction. This occurs when sunlight encounters tiny ice crystals or droplets and bends around them, separating the light into different colours.
The effect is particularly noticeable in newly formed clouds where the ice crystals or droplets are relatively uniform in size. Those conditions allow the different wavelengths of visible light to spread in a more organised way, producing bands, waves or patches of colour.
According to the Bureau of Meteorology, smaller clouds can provide favourable conditions because more rays of sunlight are able to pass through the formation and undergo diffraction around individual particles.
The result can range from subtle pastel shades to vivid displays of pink, green, blue, yellow and purple, depending on the cloud’s structure, the size of its particles and the position of the sun.
How Iridescent Clouds Differ From Rainbows
Despite their similar appearance, iridescent clouds and conventional rainbows are created through different optical processes.
Cloud iridescence primarily results from diffraction, with sunlight bending around tiny ice crystals or water droplets. This causes colours to spread across the cloud in rings, waves or irregular patches.
A rainbow, by comparison, forms when sunlight enters water droplets and undergoes both refraction and internal reflection. The light is separated into its component colours, producing the familiar sequence of relatively distinct and orderly bands.
A Fleeting Sight in Australian Skies
Iridescent clouds can occur in Australia when the right combination of high-altitude cloud, sunlight and similarly sized particles develops.
However, the effect can disappear rapidly as clouds move, grow or change structure. The viewing angle also matters, meaning the colours may be visible from one location but difficult to detect from another.
That helps explain why the phenomenon can be relatively common from a meteorological perspective while still seeming unusual to people on the ground.
For residents who spotted the clouds across Melbourne, the weekend display offered a brief glimpse of one of the atmosphere’s more colourful optical effects.
The Victorian sightings highlight how ordinary high-altitude clouds can produce an unusual spectacle when sunlight, ice crystals and atmospheric conditions align, transforming patches of cirrus into a fleeting rainbow-coloured display.
Cory Weinberg is a contributor to Sproutwired.com, covering a wide range of topics including news, politics, business, technology, sport, entertainment and lifestyle. He focuses on delivering clear, balanced reporting that helps readers stay informed about current events and emerging developments. Cory’s work highlights relevant stories, practical insights and important issues affecting communities and industries, with an emphasis on accuracy, clarity and information that readers can trust.
