Nikon D90. 1100mm f10 lens. 1/4000s @ ISO100 (stopped down by five stops). No filters. Minimal image processing.
The Omega Sun is a reflection effect seen after Sunrise or before Sunset. The lower limb of the Sun is reflected in thick layer of atmosphere cose to the horizon.
After this photo was taken and several seconds before actual Sunset, there were several vivid green scintillations before a final green flash ‘flourish’ as the Sun set.