Fata Morgana

A fata Morgana is an optical phenomenon which results from a temperature inversion. Objects on the horizon appear elongated, like "fairy tale castles." The cold dense air near the surface of the ground acts as a lens. Fata Morgana are usually seen in the morning after a cold night which has resulted in the radiation of heat into space. It is common in high mountain valleys, such as the San Luis Valley of Colorado where the effect is exaggerated due to the curvature of the floor of the valley canceling out the curvature of the Earth.

And forever before me gleams,
The shining city of song,
In the beautiful land of dreams.
But when I would enter the gate
Of that golden atmosphere,
It is gone, and I wonder and wait
For the vision to reappear. (Fata Morgana by Henry Wadsworth Longfellow)