Residents in several Melbourne suburbs were treated to an unusual natural spectacle over the weekend, with colourful iridescent clouds appearing across parts of Victoria. The phenomenon was photographed in suburbs including Mount Waverley and Caroline Springs, creating rainbow-like patterns that briefly appeared across the sky.

The unusual clouds are known as iridescent clouds and occur when sunlight interacts with tiny ice or water particles within clouds. The interaction causes sunlight to diffract, producing a range of colours that can resemble a rainbow. Unlike an ordinary rainbow, however, the colours do not necessarily appear in a fixed or clearly defined sequence.

The phenomenon was visible after cirrus clouds appeared over Victoria. Cirrus clouds form high in the atmosphere and are made primarily from ice crystals. Under the right conditions, these crystals can interact with sunlight in a way that produces the colourful visual effect.

Meteorologists say iridescent clouds are not especially uncommon in Australia, but they are often difficult for people to see because the effect can be extremely brief. The right combination of cloud structure, sunlight and similarly sized ice crystals is needed for the colours to become visible.

For people who happened to look toward the sky at the right moment, the result was a striking display of pink, blue, green and other shades spreading through the clouds. Photographs taken around Melbourne captured the phenomenon and quickly highlighted how unusual the clouds can appear.

The science behind the display is different from the process that creates a traditional rainbow. Rainbows are produced through refraction and reflection of sunlight in water droplets, creating familiar bands of colour. Iridescent clouds instead gain their appearance primarily through diffraction, where light bends and spreads as it encounters tiny particles or ice crystals.

The size and arrangement of the crystals are important. When the particles are relatively similar in size and positioned appropriately within a cloud, sunlight can be diffracted in a way that produces colourful rings or wave-like patterns.

The phenomenon can sometimes be confused with another atmospheric optical effect known as a sun dog. Sun dogs generally appear as bright areas or patches of light positioned to either side of the sun and are associated with ice crystals at lower levels of the atmosphere. Iridescent clouds, by comparison, can appear directly within or around clouds at higher levels.

The colourful clouds provided Melbourne residents with a rare opportunity to observe atmospheric science happening naturally above the city. Although the display was temporary, photographs from the weekend captured the unusual colours and allowed the spectacle to be shared more widely.

The event is another reminder that unusual weather and atmospheric conditions can create striking scenes across Melbourne without warning. For photographers and residents interested in natural phenomena, the appearance of iridescent clouds can be particularly rewarding because the colours can disappear as quickly as they emerge.

The phenomenon was observed across parts of Victoria over the weekend, with Melbourne suburbs among the locations where the colourful clouds were photographed.