Sunset Colors on Four Different Evenings

December 16, 2014

Sunset Colours
   Sunset Colours 2

: Mary Brown
Summary Authors: Mary Brown; Jim Foster

These images taken during this past summer on four different evenings show the wonderful variety of colors displayed at sunset. Each evening's color is different. For the sequence at top I used an intervalometer to take pictures at consistent intervals over a period of time. Then, I combined the pictures to display each evening's sunset in one image -- approximately 250 pictures for a single sunset. This approach is similar to taking images for a time-lapse. But instead of making a time-lapse video, I used a program called StarStax to combine the pictures into one image. The bottom sequence features just a single picture from each of the series of shots used for the intervalomter/StarStax images.
At sunrise and sunset, the increasing path length of sunlight acts to redden the colors we see. However, memorable sunsets usually require an abundance of aerosols (fine dust and ash particles, for instance) and or clouds positioned in such a way to take advantage of the lingering sunlight. Shorter wavelengths of sunlight (greens, blues, and violets) are more readily scattered from our view by minute particles in the atmosphere than are the longer wavelengths (reds, oranges and yellows). Moreover, ozone and water vapor absorb certain green and blue wavelengths, which can further redden the sky.
"It does no harm to the romance of the sunset to know a little bit about it." -- Carl Sagan