7 - Atmospheric halos

Summary

This morning, 26^th of October, being on the River coming up to London, about half an Hour past Ten, the Sun being then about twenty Degrees high, I observed a Circle about the Sun, which is by no means unusual, when the Air in Chilly Weather, such as is now, is replete with snowy Particles; which Circle was of the size it always appears in, about 23 Degrees from the Sun, and faintly ting'd with the Colours of the Iris. When this circle happens, I always look out, to see whether any other Phenomena that sometimes attend it did at that time appear, such as Parhelia, and other coloured Circles, concentrick with the Sun …

Edmund Halley, Letter to the Royal Society, 1720, Philosophical Transactions of the Royal Society, vol. 3, pp. 211–12

Ice halos

Take the advice of the engaging Edmund Halley (of comet fame), and ‘… always look out …’ for ice halos in the sky. Sooner or later you're bound to develop a nose for them, just as he did. Despite being an eminent astronomer and mathematician, and a leading member of the English scientific establishment of his day, Halley was never so busy that he hadn't time to glance up at the sky in search of halos and rainbows, and share his observations with others in his characteristically informal, easy-going manner.