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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 cool 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 XX12 promotes good air ventilation
of the optics, but it will still require at least 30 minutes or so to
equilibrate. If the temperature difference between indoors and
outdoors is more than 40°, it will likely take longer. In the win-
ter, 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 XX12 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" Deep View eyepiece, which provides a mag-
nification of 43x, and a 10mm focal length 1.25" Sirius Plössl
eyepiece, which provides a magnification of 150x. 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
24
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
objects like planets and double stars. The Moon also takes
higher magnifications well.
Deep sky objects, however, typically look better at medium
or low magnifications. This is because many of them are
quite faint, yet have some extent (apparent width). Deep sky
objects will often disappear at higher magnifications, since
greater magnification inherently yields dimmer images. This
is not the case for all deep sky objects, however. Many galax-
ies are quite small, yet are somewhat bright, so higher power
may show more detail.
The best rule of thumb with eyepiece selection is to start with
a low power, wide field, and then work your way up in magnifi-
cation. If the object looks better, try an even higher magnifica-
tion. If the object looks worse, then back off the magnification
a little by using a longer focal length eyepiece.
astronomical objects
Now that you are all setup and ready to go, one critical deci-
sion must be made: what to look at?
A. The Moon
With is rocky and cratered surface, the Moon is one of the
most interesting and easy subjects to view with your tele-
scope. The best time to view it is during its partial phases
when shadows fall on the craters and canyon walls to give
them definition. While the full moon may look like a tempting
target, it is not optimal for viewing. The light is too bright and
surface definition is low.
Even at partial phases the Moon is very bright. Use of an
optional Moon filter helps to dim the glare. It simply threads
onto the bottom of the eyepiece. You'll find the Moon filter
improves viewing comfort, and helps bring out the subtle fea-
tures on the lunar surface.
B. The Sun
You can change your nighttime telescope into a daytime Sun
viewer by installing an optional solar filter over the front open-
ing of the telescope. The primary attraction is sunspots, which
change shape, appearance, and location daily. Sunspots are
directly related to magnetic activity in the Sun. Many observ-
ers like to make drawings of sunspots to monitor how the Sun
is changing from day to day.
Important Note: Do not look at the Sun with any optical
instrument without a professionally made solar filter, or
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