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I noticed in the middle of last summer an interesting
phenomenon, which I couldn't satified explain.
My observations were made from the moving bus during
about 70-90 minutes. In the beginning the Sun was in
about 20 degrees altitude and I saw red tint in the
horizon just below the Sun. The color was seen in
the high clouds, cirrus or so. There were also some
lower cumulus clouds in the area, but they weren't
red. The hight on the red area was about 4 degrees
and the width about 20-30 degrees. The red tint got
smoothly faint when going outside from the horizont
point below the Sun.
When the Sun goes lower, there was not markable
changes in the size of the area. Perhaps the size
increased a little. There were cirrus clouds also
in the larger area, but that defined area was red
coloured.
The first idea was that this was halo: distorted
22 degree lower tangential arc, but in the end of
the observation the Sun was only in <15 degrees
altitude and the red clours was not halo-like
(I have seen several low Sun halos).
I guess this is connected to ordinary twilight
effects, but I haven't noticed earlier color
phenomenon like this.
-Veikko-
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