| Sunset at Pointe de la Torche
, France imaged
by Laurent Laveder (PhotoAstronomique.net)
in August '04. The faint lines have been added to indicate layers
of different temperature in the atmosphere. As the sun's image sinks through
them it is miraged into fantastical ever changing shapes. The slices show
descending erect images of the solar disk and ascending inverted images. Images ©Laurent Laveder, shown with permission.
A setting sun distorted
and seemingly cut into horizontal slices is a sign that one or
more temperature inversion layers are at work. The layers are sometimes
made visible (1,2)
by the dust and aerosol they trap and greater refraction.
Sunlight is refracted by the different density layers sometimes
sufficiently strongly to produce mock-mirages (ray
The mirages are most apparent when the progress of the sinking
sun is closely watched (eye care!).
A single mock-mirage has two erect images and an
inverted image. Sections of the sun will often be seen sinking
and rising in the layers. Where an image is rising, we are
seeing a section of an inverted solar disk.
Sometimes the temperature, and thus density, differences are so
great that rays are trapped within layers. Ducting is said to occur
and the trapped rays might travel large distances before escaping.
Here are two ducted M-Mir sunsets 1,2.
Mock-mirage sunsets are very sensitive in their appearance to
your height. You must be above the inversion layer but not necessarily
physically very high because inversions can be very
close the the land or sea surface. Two views of the same sunset are
The top of a mock-mirage sunset sometimes produces a single or even
multiple green and blue flashes. These
are less pronounced than the classical I-Mir
flash and are more often photographed than observed