Is this a Fata Morgana? I took this photo. Above the horizon there is a thick layer that looks like a cloud, but it surely isn't. Is this a Fata Morgana? What do you think?
EDIT: I think the more appropriate name is superior mirage, not Fata Morgana.
The Image

 A: My reply does not claim to be the correct answer.  Rather, because it intrigues me, it may start a discussion as it does contain speculations, too.  Nor I am a native English speaker.
From observation of the picture, the sun is below the horizon.  The horizontal line we call horizon depends on the level of elevation we stand on.
If the picture were taken on a celestial object without a significant atmosphere (like the moon of the earth), the picture likely would display the sky of night with light emitting objects (stars) or light reflecting ones like satellites.  However, our earth possess an humid atmosphere.  On droplets of water in higher layers of the atmosphere (vide supra), light emitted by the sun is subject of diffraction. Beside the blue sky, this offers us phenomena called twilight/gloaming/crepuscule, etc. Returning to the picture, diffraction deviates the pathway of the light, eventually providing some remnant light passing towards the observers direction.
Yet: why there is a less bright layer just on top of the sea's surface and below the partially open sky?  At least some clouds are depicted in the foreground of the picture.  This is likely to happen in the early evening of a sunny day; warmer sea water still evaporates into the already less warmer layers of air, yielding clouds.  Light, diffracted and diffracted again in these clouds eventually does not get its way to the observer's perspective, especially at this angle of observation. For the observer's point of view, this appears like absorption of light, and thus darkens this layer.  If you were underneath these ``dark clouds at the horizon'' not-necessarily would be pitch-dark.
Does this dark line possess a particular name?  Beside dusk?  Likely this were an answer for a trained physicist.  On the other hand, I would not call it a Fata Morgana.  This qualification is based on the absence of any object appearing (at least in some part) partially mirrored upside-down.  On the picture, however, I do not spot a boat, nor a bridge, nor a lighthouse nor an other object indicating to me the requirements met to actually yield a Fata Morgana.
