Mushroom sunset La Coruna, Spanish Atlantic Coast . Imaged by Oscar Blanco 25th October '05. Image ©Oscar Blanco. As the upper sun descends a second sun climbs from the ocean. The lower sun fragment is a rising inverted image of the lower limb. This remarkable mock-mirage sunset was made by a strong temperature inversion likely produced by warm air from onshore overlaying cooler maritime air. The cooler air below the inversion is visible a a darker band (greater optical extinction) above the horizon. Its upper edge is is lit by the 'tin-hat' effect characteristic of strong inversions. The inversion here is so strong that 'ducting' is taking place. Rays are trapped within the inversion layer and travel considerable distances before escaping. Oscar estimates that he was no more than 30m above the ocean surface and Andrew Young estimates that the top of the inversion layer was ~5m below.