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18
Seeing Conditions
Viewing conditions affect what you can see through your
telescope during an observing session. Conditions include
transparency, sky illumination, and seeing. Understanding
viewing conditions and the effect they have on observing will
help you get the most out of your telescope.
Transparency
Transparency is the clarity of the atmosphere which is affected
by clouds, moisture, and other airborne particles. Thick cumulus
clouds are completely opaque while cirrus can be thin, allowing
the light from the brightest stars through. Hazy skies absorb
more light than clear skies making fainter objects harder to see
and reducing contrast on brighter objects. Aerosols ejected
into the upper atmosphere from volcanic eruptions also affect
transparency. Ideal conditions are when the night sky is inky black.
Sky Illumination
General sky brightening caused by the Moon, aurorae, natural
airglow, and light pollution greatly affect transparency. While
not a problem for the brighter stars and planets, bright skies
reduce the contrast of extended nebulae making them difficult,
if not impossible, to see. To maximize your observing, limit
deep sky viewing to moonless nights far from the light polluted
skies found around major urban areas. LPR filters enhance deep
sky viewing from light polluted areas by blocking unwanted
light while transmitting light from certain deep sky objects. You
can, on the other hand, observe planets and stars from light
polluted areas or when the Moon is out.
Seeing
Seeing conditions refers to the stability of the atmosphere
and directly affects the amount of fine detail seen in extended
objects. The air in our atmosphere acts as a lens which bends
and distorts incoming light rays. The amount of bending
depends on air density. Varying temperature layers have
different densities and, therefore, bend light differently. Light
rays from the same object arrive slightly displaced creating an
imperfect or smeared image. These atmospheric disturbances
vary from time-to-time and place-to-place. The size of the air
parcels compared to your aperture determines the “seeing”
quality. Under good seeing conditions, fine detail is visible
on the brighter planets like Jupiter and Mars, and stars are
pinpoint images. Under poor seeing conditions, images are
blurred and stars appear as blobs.
The conditions described here apply to both visual and
photographic observations.
seeing condiTions direcTLy AFFecT iMAge quALiTy. These drAwing rePresenT A PoinT source (i.e., sTAr)
under BAd seeing condiTions (LeFT) To exceLLenT condiTions (righT). MosT oFTen, seeing condiTions
Produce iMAges ThAT Lie soMe where BeTween These Two exTreMes.
TelesCope maInTenanCe
While your LCM telescope requires little maintenance, there
are a few things to remember that will ensure your telescope
performs at its best.
Care and CLeaning oF The opTiCS
Occasionally, dust and/or moisture may build up on the lens of
your telescope. Special care should be taken when cleaning any
instrument so as not to damage the optics.
Ifdusthasbuiltupontheoptics,removeitwithabrush(made
ofcamel’shair)oracanofpressurizedair.Sprayatanangle
to the lens for approximately two to four seconds. Then, use
an optical cleaning solution and white tissue paper to remove
any remaining debris. Apply the solution to the tissue and then
apply the tissue paper to the lens. Low pressure strokes should
go from the center of the corrector to the outer portion. Do
NOT rub in circles!
You can use a commercially made lens cleaner or mix your
own. A good cleaning solution is isopropyl alcohol mixed with
distilled water. The solution should be 60% isopropyl alcohol
and 40% distilled water. Or, liquid dish soap diluted with water
(acoupleofdropsperonequartofwater)canbeused.
To minimize the need to clean your telescope, replace all
lens covers once you have finished using it. This will prevent
contaminants from entering the optical tube.
CoLLiMaTion
The optical performance of your LCM telescope is directly related
to its collimation, which is the alignment of its optical system. Your
telescope was collimated at the factory after it was completely
assembled. However, if the telescope is dropped or jarred
severely during transport, it may have to be collimated. The LCM
60, 70, 80 and 90 are two refractor type telescopes that have
The view oF A coLLiMATed TeLescoPe As seen Through
The Focuser oF The LcM 76/114 reFLecTor TeLescoPe.
20


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