When the Sun is low in the sky, its shifting colours can teach us about the heights and consistencies of clouds, for the sweep of light as the Sun comes up or sinks tends to colour low, mid-level, and high clouds differently.

Take this sunset, spotted by Tom Bean (Member 41,135) over Upper Lake Mary, south of Flagstaff, Arizona, US. The mid-level Altocumulus cloudlets in the foreground are catching the last of the ruby rays. The Sun’s just over the horizon, and it is painting their bases and far sides a deep crimson due to the long journey of its light through dense, low atmosphere to reach them. The bruised purple of their shaded sides reveals that these are droplet clouds, which always look more solid than ice-crystal ones. Were any low-level clouds also present – Cumulus or Stratocumulus, perhaps – they’d be completely in shadow at this time of the evening.

Off in the distance, more delicate cloud streaks can be seen. Though they appear at the bottom of the image, we know they must be the high ice-crystal cloud Cirrus. Their golden colours show that the light reflecting off them has reached us through less-dense, higher atmosphere. Their minimal shading suggests they are made of ice crystals rather than droplets.

We’ve found that the Sun’s best cloudspotting lessons are always timetabled at dawn and the day’s end.