6 - Coronae and glories

Summary

For in June, 1692, I saw by reflexion in a vessel of stagnating water three halos, crowns, or rings of colours about the Sun, like three little rainbows, concentric to his body. The colours of the first or innermost crown were blue next the Sun, red without, and white in the middle between the blue and red. Those of the second crown were purple and blue within, and pale red without, and green in the middle. And those of the third were pale blue within, and pale red without; these crowns enclosed one another immediately, so that their colours proceeded in this continual order from the Sun outward: blue, white, red; purple, blue, green, pale yellow and red; pale blue, pale red … like crowns appear sometimes about the Moon.

Isaac Newton, Optics, Book 2 Part 4, G. Bell & Sons, 1931

Coronae

When a Moon that is full, or nearly full, is seen though a thin veil of altocumulus cloud, you may sometimes notice that it is surrounded by a series of more-or-less concentric, coloured rings. These are known as diffraction coronae. Corona is Latin for crown. Coronae also form around the Sun in the same circumstances, though you are unlikely to notice any colours in clouds that lie close to the Sun because of the brightness of the clouds.