A remarkable double sunset mirage
at Paranal Observatory high in the Atacama Desert, Chile
Arnold of Observatoire de Haute-Provence,
France saw this spectacular apparition in January
2002 at the site of the European
Southern Observatory Very Large Telescope
array of four 8.2 meter reflectors. He was at an
altitude of 2,400 meters as the sun set over the
Pacific Ocean whose shore was 12 km away.
The upper, very bright, image is
a very highly flattened sun setting through a strong inversion
layer. The layer is visible as a hazy band
each side of the sun.
Details below this layer are partially
hidden by the band of marine stratus cloud which is capped
by the upper inversion.
The puzzle is the relatively undistorted second erect
image of the sun setting into the ocean horizon below the
clouds. At Paranal's altitude, this sea horizon (including
refraction effects) might be more than 80 miles distant
and well below the astronomical horizon. To explain the
lower sun we must invoke a second, lower and stronger inversion
layer. This produces the lower erect image and possibly
parts of an inverted image hidden by the clouds. The lower
image is less distorted than is usual in mock-mirages because
it is viewed considerably below the astronomical horizon
and the rays therefore pass through the air layers less
'edge-on'. My thanks to Andrew
Images ©Luc Arnold, shown with permission.