Orion SKYQUEST XT10 CLASSIC - Manual (Page 13)

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matter. Your eyes take about 30 minutes to reach perhaps 80%
of their full dark-adapted sensitivity. Many observers 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. 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 light
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, or you can cover the front of a
regular flashlight with red cellophane or paper. Beware, too,
that nearby porch and streetlights and automobile headlights
will spoil your night vision.
tracking celestial objects
The Earth is constantly rotating about its polar axis, complet-
ing one full rotation every 24 hours; this is what defines a “day.”
We do not feel the Earth rotating, but we can tell that it is at
night by seeing the apparent movement of stars from east to
west. This movement translates into a rate of approximately
.25° per minute, or 15 arc-seconds per second. (There are 60
arc-minutes in 1°, and 60 arc-seconds in one arc-minute.) This
is called the sidereal rate.
When you observe any astronomical object, you are watching
a moving target. This means the telescope’s position must be
continuously updated over time to keep an object in the field
of view. This is easy to do with the SkyQuest XT because of its
smooth motions on both axes. As the object moves off toward
the edge of the field of view, you just lightly nudge the tele-
scope to bring it back to the center.
You will notice that it is more difficult to “track” objects when
the telescope tube is aimed nearly straight up. This is inherent
to the basic design of the Dobsonian, and stems from the fact
that there is very little mechanical leverage to move in azimuth
when the tube is in a near vertical position. To gain more lever-
age, try grasping the tube close to the altitude side bearings
with both hands.
Remember that objects appear to move across the field of
view faster at higher magnifications. This is because the field
of view becomes narrower.
Eyepiece selection
By using eyepieces of varying focal lengths, it is possible to
attain many magnifications with the SkyQuest XT. The tele-
scope comes with one high-quality Sirius Plössl eyepiece: a
25mm, which gives a magnification of 48x. Other eyepieces
can be used to achieve higher or lower powers. It is quite com-
mon 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.
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 galaxies 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 magnifica-
tion. If the object looks better, try an even higher magnification.
If the object looks worse, then back off the magnification a
little by using a lower-power eyepiece.
using 2" Eyepieces (Xt8 and Xt10)
The SkyQuest XT8 and XT10 Crayford focusers are capable
of accepting optional 2" eyepieces. To use 2" eyepieces you
must remove the 1.25" adapter from the focuser by turning
the two thumbscrews that hold it in place. Once this adapter
is removed, insert a 2” eyepiece directly into the eyepiece
holder and use the same thumbscrews to secure the larger
eyepiece.
2" eyepieces are desirable because they provide a wider field of
view than 1.25" eyepiece. Many observers own at least one 2"
eyepiece to yield the largest field of view possible for looking at
wide deep-sky objects, such as open star clusters or gaseous
nebulae. You’ll be stunned at the large fields of view that 2" eye-
pieces deliver. You’ll feel like you’re floating in space!
Now that you are all set up and ready to go, one critical
decision 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 scope.
The best time to view it is during its partial phases when
1.9
1.9
1.7
4.9
2.4 3.4
2.5
2.4
Figure 19. Megrez connects the Big Dipper’s handle to it's “pan”.
It is a good guide to how conditions are. If you can not see Megrez
(a 3.4 mag star) then conditions are poor.