The photo shows the setting sun, severely flattened by stratified layers of air at different densities caused by the uneven mixing of a new cold front with a much warmer lingering mass. As the Sun was setting over the sea, it was gradually distorted by differential refraction and acquired many different shapes, including: mushroom, pancake, disk and finally a very thin rectangle. It was indeed a delightful treat to end the day. Note the dark streak at lower left of the disk that actually corresponds to the distorted image of three sunspots of Active Region 2778.

Handheld Nikon CoolPix P900 camera

Photoscape used for improved contrast