SAXON TRAVELLER SCOPE INSTRUCTION MANUAL
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1. Sky 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 observe 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.
2. Selecting 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. If you try to observe on any structure, or even a sidewalk, movements you
make may cause the telescope to vibrate. Pavement and concrete can also radiate stored heat which
will affect observing.
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.
3. Choosing the best time to observe
The best conditions will have still air, and obviously, a clear view of the sky. It is not necessary that the
sky be cloud-free. Often broken cloud conditions provide excellent seeing. Do not view immediately
after sunset. After the sun goes down, the Earth is still cooling, causing air turbulence. 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.
4. Cooling the telescope
Telescopes require at least 10 to 30 minutes cooling down to outside air temperature. However this
may take longer if there is a big difference between the temperature of the telescope and the outside air.
This minimizes heat wave distortion inside telescope tube (tube currents). Allow a longer cooling time
for larger optics. If you are using an equatorial mount, use this time for polar alignment.
5. Using your eyes
Do not expose your eye to anything except red light for 30 minutes prior to observing. This allows your
pupils to expand to their maximum diameter and biochemical light adaptation to occur. It is important to
observe with both eyes open. This avoids fatigue at the eyepiece, allows you to check against reference
material, and is a good habit to develop if you sketch at the eyepiece. If you find this too distracting,
cover the unused 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.
Observing the Sky
