Orion 9966 Instruction Manual page 15

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
magnification. 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.
Use of 2" Eyepieces
The SkyQuest XT12 comes with a large format focuser
(Figure 16) as standard equipment. Because of its large size,
it is able to accept eyepieces that have a 2" barrel diameter.
2" eyepieces are desirable because they allow for a wider
field of view than 1.25" eyepieces. 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 clus-
ters and gaseous nebulae. 2" eyepieces can also give nice
views of the Moon.
To use a 2" eyepiece, simply remove the 1.25" eyepiece
adapter from the end of the focuser drawtube. You must first
loosen the two thumb screws on the 2" eyepiece adapter
to do this. Now, insert a 2" eyepiece into the focuser, and
secure it with the two thumb screws. Focus the eyepiece as
described previously.
You'll be stunned at the wide fields of view that 2" eyepieces
can deliver. It will make you feel like you're floating through
space!
Astronomical Objects
Now that you are all set up 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 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 to 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 of 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 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 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. Also, be sure to cover
the finder scope, or better yet, remove it altogether.
C. The Planets
The planets don't stay put like the stars, so to find them you
should refer to Sky Calendar at our website OrionTelescopes.
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 XT12 is capable of
showing you these planets in some detail. Other planets
may be visible but will likely appear starlike. Because plan-
ets are quite small in apparent size, optional higher power
eyepieces are recommended and often needed for detailed
observations. Not all the planets are generally 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 moon:
Io, Callisto, Europa, and Ganymede. Higher power eyepieces
should bring out the cloud bands on the planet's disk and the
Great Red Spot.
SATURN The ringed planet is a breathtaking sight. The tilt
angle of the rings varies over a period of many years; some-
times they are seen edge-on, while at other times they are
broadside and look like giant "ears" on each side of Saturn's
disk. A steady atmosphere (good seeing) is necessary for a
good view. Look closely and you should see the Cassini divi-
sion, a thin, dark gap in the rings. You should also see one
or more of Saturn's moons, which look like faint stars. The
brightest is the moon Titan.
VENUS At its brightest, Venus is the most luminous object in
the sky, excluding the Sun and the Moon. It is so bright that
sometimes it is visible to the naked eye during full daylight!
Ironically, Venus appears as a thin crescent, not a full disk,
when at its peak brightness. Because it is so close to the Sun,
it never wanders too far from the morning or evening horizon.
No surface markings can be seen on Venus, which is always
shrouded in dense clouds.
MARS The Red Planet makes a close approach to Earth
every two years. Observing Mars is most favorable at these
times. You should see salmon-colored disk with some distinct
dark patches, and you may be able to spot a whitish polar
ice cap. To see surface detail on Mars, you will need a high
power eyepiece and very steady air!
D. The Stars
Stars will appear as tiny points of light. Even powerful tele-
scopes cannot magnify stars to appear as anything more
than pinpoints. You can, however, enjoy the different colors
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