When noticing the title of Blue Sun sets behind the Pyramids in Egypt
at Redidt.com, I believed this may be a unique spectacular phenomenon of the Sun, but it seems not, it's a result of air pollution. From Coasttocoastam.com
PyramidCam captures a live image of the pyramids every 30 seconds. This particular image, saved by Tom Hartlove on December 14, 2006, is one of only a few ever documented occurrences of a blue sun
. Tom happened to run across the image a few days ago in his photo archives and sent it to an expert in atmospheric physics to find out what might have caused it. Here was the reply:
"A very rare phenomenon known as a 'blue sun.' These have been observed from time to time around the world. The most recent widely accepted documentation of a blue sun occurred in September 1950 in Edinburgh, Scotland. A discussion of that event appears in Craig Bohren's book, 'Clouds in a Glass of Beer,' on page 91."
The main cause is thought to be smoke in the atmosphere. From time to time smoke from farmers burning brush between the camera location and the pyramids' plateau rises to camera level and is apparent on many of our images. We have also captured long plumes of smoke visible behind the pyramids, particularly in winter when farmers burn stubble in the fields in the Delta and around Cairo.