January 28, 2008
The photo above shows a spectacular sunset taken from Great Falls, Montana in July of 2002. Photographing the array of orange, yellow and purple colors in the western sky, I couldn't help but notice the striking golden strand at left center. It's likely a contrail that appears vertical due to my perspective. Note the apparent counterclockwise spiral in the upper part of the structure.
If aerosols are introduced into the atmosphere during the day, either by human activities such as dust from harvesting crops or from volcanic eruptions or other natural sources then the green colors at the mid-range of the visible spectrum may be more readily attenuated allowing deeper oranges and reds to predominate in the sky at sunset.