Base was a normal ordinary sunny day in Singapore (sun not in shot), with powerlines and such in the way. Cut, patched, and masked the new sky in, placed a lensflare sun, then applied a warming photofilter to the city, then used levels to make it dark, while keeping the brights bright. Finally, I added a Godray effect to make a neat washout effect around the "Sun."
A tutorial for that Godray effect can be found here: http://www.filedropper.com/godraytutorial