Orion XT4.5 Instruction Manual page 11

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 XT4.5. The
telescope comes with two high-quality Sirius Plössl eye-
pieces: a 25mm, which gives a magnification of 36x, and a
10mm, which gives a magnification of 91x. Other eyepieces
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 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 magni-
fication. 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.
Now that you are all set up and ready to go, one critical deci-
sion must be made: what to look at?
What to Expect
So what will you see with your telescope? You should be able
to see bands on Jupiter, the rings of Saturn, craters on the
moon, the waxing and waning of Venus, and possibly hun-
dreds of deep sky objects. Do not expect to see any color as
you do in NASA photos, since those are taken with long-
exposure cameras and have 'false color' added. Our eyes are
not sensitive enough to see color in deep-sky objects except
in a few of the brightest ones.
Remember that you are seeing these objects using your own
telescope with your own eyes! The object you see in your
eyepiece is in real-time, and not some conveniently provided
image from an expensive space probe. Each session with
your telescope will be a learning experience. Each time you
work with your telescope it will get easier to use, and stellar
objects will become easier to find. Take it from us, there is big
difference between looking at a well-made full-color NASA
image of a deep-sky object in a lit room during the daytime,
and seeing that same object in your telescope at night. One
can merely be a pretty image someone gave to you. The
other is an experience you will never forget!
A. The Moon
With its rocky surface, the Moon is one of the easiest and
most interesting targets to view with your telescope. Lunar
craters, marias, and even mountain ranges can all be clearly
seen from a distance of 238,000 miles away! With its ever-
changing phases, you'll get a new view of the Moon every
night. The best time to observe our one and only natural
satellite is during a partial phase, that is, when the Moon is
NOT full. During partial phases, shadows are cast on the sur-
face, which reveal more detail, especially right along the
border between the dark and light portions of the disk (called
the "terminator"). A full Moon is too bright and devoid of sur-
face shadows to yield a pleasing view.
Use an optional Moon filter to dim the Moon when it is very
bright. It simply threads onto the bottom of the eyepieces
(you must first remove the eyepiece from the focuser to
attach a filter). You'll find that a Moon filter improves viewing
comfort, and also helps to bring out subtle features on the
lunar surface.
B. The Sun
You can change your nighttime telescope into a daytime Sun
viewer by installing an optional full-aperture solar filter over
the front opening of a SkyQuest XT4.5. The primary attraction
is sunspots, which change shape, appearance, and location
daily. Sunspots are directly related to magnetic activity in the
Sun. Many observers 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
permanent eye damage could result.
C. The Bright Planets
The planets don't stay put like the stars, so to find them you
should refer to Sky Calendar at our website (www.tele-
scope.com), or to charts published monthly in Astronomy, Sky
& Telescope, or other astronomy magazines. Venus, Mars,
Jupiter, and Saturn are the brightest objects in the sky after
the Sun and the Moon. Your SkyQuest XT is capable of show-
ing you these planets in some detail. Other planets may be
visible but will likely appear starlike. Because planets are
quite small in apparent size, optional higher-power eyepieces
are recommended and often needed for detailed observa-
tions. Not all the planets are usually visible at any one time.
JUPITER The largest planet, Jupiter, is a great subject for
observation. You can see the disk of the giant planet and
watch the ever-changing positions of its four largest moons—
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