What is Seeing?
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There are some terms you need to be familiar with to understand comments you are likely to read about observing.
One is seeing. Seeing is a reference to the ability to see details through the atmosphere. It's often given on a 1 to 10 scale, 10 being perfect seeing, and 1 being very poor, with little detail visible.
The seeing is affected by movement of air cells in the atmosphere. The cells are often different temperature and possibly different in other atmospheric properties. When looking up through the atmosphere, one looks through many air cells.
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These cells move around, causing the blurring and shifting in lunar and
planetary images. The smaller the telescope you use, the larger are the scale
of the disturbances seen.
How Does Seeing Affect What I Can See With My Telescope?
With my 2 inch refractor and medium to poor seeing I can see waves of motion
when I'm observing the moon. The more the turbulence, the greater the apparent
motion. The motion disturbances are larger than the craters I'm trying to
observe, so they don't limit the details I'm able to see. They are only a
distraction, not a limit to the details I'm trying to perceive.
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When I look at the moon with my 6 inch telescope, the waving phenomena are
smaller in apparent size, being on the order of the smaller objects I want to
see. In fact, the atmospheric motion forms a limit to the smallest details I'm
able to resolve.
This explains why with medium to small telescopes, there are more evenings
of acceptable seeing. The motion effects must be virtually gone for larger (8
inch or better) telescopes to be able to function up to their potential.
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What is Transparency?
Another term you'll see when reading about observing is transparency.
Transparency has to do with the ability to see dim objects through the
atmosphere. There are many atmospheric phenomenon that can adversely affect
transparency.
If you live in or near a city, pollution can reduce transparency. Thin, high
altitude clouds can affect transparency. Forest fires can put up enough
material to affect seeing over a very wide area.
Transparency is also often indicated with a 1 to 10 rating, 10 being the best transparency.
If transparency is low, then your ability to detect dim objects such as galaxies is
greatly reduced.
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Recording the Observations
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If you find you enjoy observing, you might consider keeping a journal where
you can make notes of your observations. If you decide to do that, make the
observations more useful by annotating (with a number from 1 to 10) the seeing
and transparency conditions, as well as the telescope and other equipment you
used. Consider posting your observations on your website, or join an e-group
and share your experiences there.
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Why?
First, you'll enjoy reviewing your notes when you view the same or similar
objects again later, perhaps through different conditions or a different
telescope.
Plus, we all get clouded in now and again, and reading about someone else's
observations helps make those days less terrible. Reading the observations of
others, if they are properly documented, is also helpful when you are shopping
for another telescope. It helps you visualize what you might see with different
sized and types of instruments.
Of course it's not only atmospheric conditions that affect what you will see
in the night sky. The views of different object types is also a function of the
type and size of telescope used. For observing those dim objects, you need
good transparency and a large aperture, small f ratio instrument.
To view high resolution objects such as planets, transparency is less an issue,
but you need good seeing and a telescope designed to deliver resolution.
The following table gives a listing of different telescope types and sizes in
a matrix form that suggests which telescope is good for which kind of observing.
Telescope/Observing Preference Table
One online shopping mall that has telescopes in all of these categories
is
SHOP.COM
 . They carry very good prices on instruments and telescope accessories
from Celestron, Meade, Tele Vue, Vixen, and Rigel Systems, to name a few.
Just enter astronomical telescopes, or the specific type of telescope or accessory in their search engine.
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