Stockholm Spring Sunset

Not a mirage. Also, the belief of some tourists that Scandinavia has two suns, an ordinary one and a midnight sun that only appears in summer, is untrue!  Peter Rosen imaged the sunset on the two consecutive clear days (22nd and 23rd March) closest to the spring equinox. He then superimposed them, the rightmost sun is the 23rd. In only one day the sun has climbed appreciably in the sky and the sunset point has shifted north by more than 0.75 giving an extra 5m21s of daylight. Welcome signs indeed after a long, dark and cold northern winter.      Images ©Peter Rosen, shown with permission
Mirages give multiple suns or at least multiple sun slices. But the images are almost always vertically stacked . Horizontally displaced images would need blocks of different temperature air meeting in near vertical planes. This does not happen except for example near a vertical sun-heated wall.
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Earth's axis is tilted ~23.5° to the plane of its path around the sun. At the equinox the sun rises near exactly in the east and sets at west. In the northern hemisphere the sunrise and sunset points creep northwards as spring advances making each day slightly longer. The changes are most rapid at the equinox and slow to zero at the summer solstice.