There isn't much to see here — just a red-and-green line that grows steadily shorter, with the green steadily eating into and finally overwhelming the red. This line is an enormously compressed image of part of the Sun, barely visible above the top of the duct.
In reality, the large airmass at the end of this sunset would normally have removed the green light entirely; you'd see only a red line that finally shrinks to a dot and vanishes. The green is visible in the Taylor-Matthias pictures because they were taken at very great elevation, where the extinction is much smaller.
Amazingly, this kind of sunset was photographed by John McKune in Libya on March 28th, 2006. You can see his astonishing pictures on Les Cowley's website. He's finally captured the features of this simulation that I made back in 1999.
© 1999 – 2009 Andrew T. Young