Introduction
An observer, be they at a mountain top observatory,
or in their own back yard must, at all times contend with the Earth’s
atmosphere. It is a notoriously unpredictable and limiting factor in obtaining
fine views of
the Planets, and close binary stars. Many often comment, especially here
in the UK that seeing is all too often mediocre on most nights, but what
are the factors that contribute to this?. Are there ways and signs, which
indicate whether the atmosphere, will be stable or turbulent on a given night?.
What is “seeing”?
So what exactly is atmospheric seeing? - it
is high frequency temperature fluctuations of the atmosphere, and the mixing
of air “parcels” of
different temperatures/densities. This behaviour of the atmosphere is seen
at the eyepiece as a blurred, moving, or scintillating image. There are roughly
3 main areas where Atmospheric turbulence occurs. Near ground seeing
(0 – 100metres or so.) central troposphere (100m – 2km), and
High troposphere (6-12km.) Each area exhibits different characteristics,
which are explained in more detail below. What is “seeing”?
