There have been several nice news articles about a historic halo diagram described by Eva Seidenfaden in the 1 Oct. 2011 Applied Optics feature issue on light and color in the open air.

Eva’s paper: http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-50-28-F60

News stories:

http://www.nature.com/news/2011/110930/full/news.2011.567.html

http://www.scientificamerican.com/article.cfm?id=seven-suns-of-rome-diagram-lost-document-350-years