Observing The Sky; Sky Conditions; Selecting An Observing Site; Choosing The Best Time To Observe - SKY-WATCHER CQ40 Instruction Manual

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ky conditions
Sky conditions are usually defined by two atmospheric characteristics, seeing, or the steadiness of the air, and
transparency, light scattering due to the amount of water vapour and particulate material in the air. When you ob-
serve the Moon and the planets, and they appear as though water is running over them, you probably have bad
"seeing" because you are observing through turbulent air. In conditions of good "seeing", the stars appear steady,
without twinkling, when you look at them with unassisted eyes (without a telescope). Ideal "transparency" is when
the sky is inky black and the air is unpolluted.
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electing an observing site
Travel to the best site that is reasonably accessible. It should be away from city lights, and upwind from any source
of air pollution. Always choose as high an elevation as possible; this will get you above some of the lights and
pollution and will ensure that you aren't in any ground fog. Sometimes low fog banks help to block light pollution if
you get above them. Try to have a dark, unobstructed view of the horizon, especially the southern horizon if you
are in the Northern Hemisphere and vice versa. However, remember that the darkest sky is usually at the "Zenith",
directly above your head. It is the shortest path through the atmosphere.
Do not try to observe any object when the light path passes near any protrusion on the ground. Even extremely
light winds can cause major air turbulence as they flow over the top of a building or wall.
Observing through a window is not recommended because the window glass will distort images considerably. And
an open window can be even worse, because warmer indoor air will escape out the window, causing turbulence
which also affects images. Astronomy is an outdoor activity. The best conditions will have still air, and obviously, a
clear view of the sky. It is not necessary that the sky becloud-free. Often broken cloud conditions provide excellent
seeing.
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hoosing the best time to observe
Do not view immediately after sunset. After the sun goes down, the Earth is still cooling, causing air tur-
bulence. As the night goes on, not only will seeing improve, but air pollution and ground lights will often
diminish. Some of the best observing time is often in the early morning hours. Objects are best observed as
they cross the meridian, which is an imaginary line that runs through the Zenith, due North-South. This is the
point at which objects reach their highest points in the sky. Observing at this time reduces bad atmospheric
effects. When observing near the horizon, you look through lots of atmosphere, complete with turbulence,
dust particles and increased light pollution.
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ooling the telescope
Telescopes require at least 10 to 30 minutes to cool down to outside air temperature. This may take longer if there
is a big difference between the temperature of the telescope and the outside air. This minimizes heatwave dis-
tortion inside telescope tube (tube currents). Allow a longer cooling time for larger optics. Use this time for polar
alignment.
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dapting your eyes
Do not expose your eyes to anything except red light for 30 minutes prior to observing. This allows your pupils to
expand to their maximum diameter and build up the levels of optical pigments, which are rapidly lost if exposed to
bright light. It is important to observe with both eyes open. This avoids fatigue at the eyepiece. If you find this too
distracting, cover the non-used eye with your hand or an eye patch. Use averted vision on faint objects: The center
of your eye is the least sensitive to low light levels. When viewing a faint object, don't look directly at it. Instead,
look slightly to the side, and the object will appear brighter.
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leaning your telescope
Replace the dust cap over end of telescope whenever not in use. This prevents dust from settling on mirror or lens
surface. Do not clean mirror or lens unless you are familiar with optical surfaces. Clean eyepieces with special lens
paper only. Eyepieces should be handled with care, avoid touching optical surfaces.
OBSERNING THE SKY
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