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get better later in the evening, as much of the heat absorbed
by the Earth during the day has radiated off into space. In
conditions of bad seeing, stars will twinkle and objects will
appear unsteady and blurry in the telescope.
“Transparency” is the clarity of the atmosphere, which can
be adversely affected by the presence of moisture, smoke,
and dust. All tend to scatter light, which reduces an object’s
brightness. Good transparency is desirable for astronomical
observing, especially for viewing faint objects.
One good measure of transparency is by how many stars
you can see with your unaided eyes. If you cannot see stars
of magnitude 3.5 or dimmer, then transparency is poor.
Magnitude is a measure of how bright a star is. The brighter a
star, the lower its magnitude. A good star to remember for this
is Megrez (magnitude 3.4), which is the star in the Big Dipper
that connects the handle to the “pan”
(Figure 49).
If you can-
not see Megrez, then you have fog, haze, clouds, smog, light
pollution or other conditions that are hindering your viewing.
Cooling the Telescope
All optical instruments need time to reach thermal equilibrium
with the outdoor air, which is essential for peak performance.
Images will be poor if the optics are not in equilibrium with the
outdoor temperature.
When moved from a warm indoor location to cooler outside
air (or vice-versa), a telescope needs time to equilibrate to
the outdoor temperature. The bigger the instrument and the
larger the temperature change, the more time will be needed.
The open truss tube design of the XX14i promotes good air
ventilation of the optics, but it will still require at least 30 min-
utes or so to equilibrate. If the temperature difference between
indoors and outdoors is more than 40°, it will likely take lon-
ger. In the winter, storing the telescope outdoors in a shed
or garage greatly reduces the amount of time needed for the
optics to stabilize. Also, after setting up outdoors, it is a good
idea to keep the telescope covered until the Sun sets so the
tube does not heat greatly above the temperature of the air.
The XX14i comes with a cooling accelerator fan. The fan
hastens the equilibration of the primary mirror to the ambi-
ent temperature by increasing airflow. The fan is powered
by its battery pack, which requires eight D-cell batteries (not
included). To turn the fan on, simply plug the battery pack’s
cable into the jack on the fan. Turn the fan on after setting up
the telescope outside at night, but prior to using it. When the
mirror has reached the ambient outdoor temperature, turn the
fan off by unplugging the battery pack.
Let Your Eyes Dark-adapt
Do not expect to go from a lighted house into the darkness
of the outdoors at night and immediately see faint nebulas,
galaxies, and star clusters – or even very many stars, for
that matter. Your eyes take about 30 minutes to reach per-
haps 80% of their full dark-adapted sensitivity. Many observ-
ers notice improvements after several hours of total darkness.
As your eyes become dark-adapted, more stars will glimmer
into view and you will be able to see fainter details in objects
you view in your telescope. Exposing your eyes to very bright
daylight for extended periods of time can adversely affect your
night vision for days. So give yourself at least a little while to
get used to the dark before you begin observing.
To see what you are doing in the darkness, use a red-filtered
flashlight rather than a white light. Red light does not spoil your
eyes’ dark adaptation like white light does. A flashlight with a
red LED light is ideal. Dim light is preferable to bright light.
Be aware, too, that nearby porch and streetlights and automo-
bile headlights will spoil your night vision. Close your eyes when
you hear an automobile approaching your observing site!
Eyepiece Selection
By using eyepieces of different focal lengths, it is possible to
attain many different magnifications with your telescope. The
telescope comes with two high-quality eyepieces: a 35mm
focal length 2" DeepView eyepiece, which provides a mag-
nification of 47x, and a 10mm focal length 1.25" Sirius Plössl
eyepiece, which provides a magnification of 165x. Other eye-
pieces can be used to achieve higher or lower powers. It is
quite common for an observer to own five or more eyepieces
to access a wide range of magnifications. This allows the
observer to choose the best eyepiece to use depending on
the object being viewed. At least to begin with, the two sup-
plied eyepieces will suffice nicely.
Whatever you choose to view, always start by inserting your
lowest-power (longest focal length) eyepiece to locate and
center the object. Low magnification yields a wide field of
view, which shows a larger area of sky in the eyepiece. This
makes acquiring and centering an object much easier. If you
try to find and center objects with high power (narrow field
of view), it’s like trying to find a needle in a haystack! Once
you’ve centered the object in the eyepiece, you can switch
to higher magnification (shorter focal length eyepiece), if you
wish. This is especially recommended for small and bright
Figure 49.
Megrez connects the Big Dipper’s handle to it’s “pan.”
It is a good guide to judging the transparency of the night sky. If you
cannot see Megrez (a 3.4-magnitude star), then the transparency is
poor.
1.9
1.9
1.7
4.9
2.4
3.4
2.5
2.4