People in Victoria have been spotting iridescent clouds lighting up the sky - they look pretty amazing apparently. It's a real phenomenon that happens under certain atmospheric conditions, and it's been happening recently. Cool to know what you're looking at if you spot something like that.
Cloud iridescence shows up when you've got thin clouds with water droplets all roughly the same size, and the light bends through them just right to split into those rainbow colors. It's most common in cirrocumulus or altocumulus clouds, especially near the sun but not directly in it - the geometry matters a lot. You'll see it more often in spring and early summer when atmospheric conditions line up, though it can happen anytime. Pretty cool to catch it, since it only lasts while the cloud's in that sweet spot between you and the sun.
Those are iridescent clouds, technically called cloud iridescence, and they happen when sunlight diffracts through water droplets of similar size in thin clouds - usually lenticular or altocumulus formations. The phenomenon occurs when the sun is at a specific angle (typically behind or to the side of the observer) and the cloud layer is thin enough for light to bend around the droplets without fully illuminating them. Victoria's recent conditions must have created ideal circumstances with the right cloud altitude, thickness, and sun position all aligning. It's one of those atmospheric tricks that's always happening somewhere, but you only notice it when you're in exactly the right spot at the right time, so consider yourself lucky to have caught it.
I saw something like that a few months back and spent like ten minutes just staring at it from my balcony - the colors were shifting between pink, green, and blue as the cloud drifted. The reason you're getting those rainbow patterns is that water droplets in the cloud are all pretty much the same size, and when sunlight hits them at the right angle, the light waves interfere with each other and split into those colors. It usually happens in thin, patchy clouds right after sunrise or before sunset when the sun's at a low angle, and the effect only lasts while conditions stay just right.
The main thing people miss is that you really need to be looking in the right direction at the right time - these clouds are only visible when the sun is positioned behind you and fairly low in the sky, usually within a couple hours of sunrise or sunset. If you're staring at them head-on or with the sun in front of you, you'll just see a regular cloud, even if the optical conditions are perfect. The color shift happens because water droplets of nearly uniform size scatter different wavelengths of light at slightly different angles, and that angular sweet spot is incredibly narrow. So if you've spotted one, you've basically caught a pretty specific alignment of sun position, cloud altitude, and droplet uniformity all lining up - worth the stare!
Caught one of these shimmering displays myself while out for a walk, and it really is something special - the key detail everyone should remember is that you've got maybe a narrow window of time to see them before the sun's angle shifts and the whole effect vanishes.
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