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Re: http://fer3.com/arc/m2.aspx/Indistinct-Horizon-Langley-may-2013-g23786

Indistinct horizons and also wrongly recognised horizons are
definitely relevant issues when performing measurements relative to
the apparent horizon. There are various "normal" reasons, i.e. reasons
which are not related to abnormal refraction. They depend to a great
extend on how the horizon is illuminated by the sun and the sky.

Reflecting sky:
The colour of the sky is reflecting on the water near the horizon.
What appears to be the horizon is only the place where the reflection
ends.

Cloud layer:
In an other thread Gary LaPook described it as: "The vast majority of
the time there are clouds between you and the horizon and even more
clouds beyond the horizon and the sun sinks behind the clouds, not
behind the sea horizon." The expression "vast majority" may possibly
be for a pilot. At about 4m a.s.l. where I made my observations it was
"occasionally" the case that there were no clouds at all, except a
thin cloud stripe at the horizon. The "real" apparent horizon is then
in its shadow. Depending on the illumination the cloud layer may
wrongly be taken as the horizon.

Haze / Smog:
I guess that the observation on Hawaii may have been from increased
humidity which causes haze and in metropolitan areas also smog. In
these situations haze/smog can hide the real apparent horizon.
Depending on the illumination one can see even a sharp line which
appears to be the horizon but which is only some border line of the
haze/smog (bank?).

If this should be of further interest, I could try to dig out some
photos showing these features.

Marcel

   

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