Tài liệu tham khảo WikiPedia: Hào quang ngoại tiếp http://www.meteoros.de/arten/ee07e.htm http://www.paraselene.de?uk:114200 http://www.atoptics.co.uk/halo/circsalt.htm http://www.atoptics.co.uk/halo/circum.htm http://www.atoptics.co.uk/halo/colsolat.htm
