Just to add another link.
Atmospheric Optics has some interesting topics.
"Light playing on water drops, dust or ice crystals in the atmosphere produces a host of visual spectacles - rainbows, halos, glories, coronas and many more. Some can be seen almost every day or so, some are once in a lifetime sights. Find out where to see them and how they form. Then seek and enjoy them outdoors."
http://www.atoptics.co.uk/
I've often thought it would be great to have 'dust spectacles'. Imagine you had glasses that could see a particular type of particle. You might then be able to 'see air'.
Jamie
Forum 
