The Moon; Terrestrial Viewing - Orion SkyView Deluxe 90mm 9401 Instruction Manual

show the positions of a number of interesting deep-sky
objects, with different symbols representing the different
types of objects, such as galaxies, open star clusters, globu-
lar clusters, diffuse nebulas, and planetary nebulas. So, for
example, your atlas might show a globular cluster sitting just
above the lid of the "Teapot" pattern of stars in Sagittarius. You
then know to point your telescope in that direction to home in
on the cluster, which happens to be 6.9-magnitude Messier
28 (M28).
You can see a great number and variety of astronomical
objects with your SkyView Deluxe 90mm, including:

the Moon

With its rocky, cratered surface, the Moon is one of the easiest
and most interesting targets to view with your telescope. The
best time to observe our one and only natural satellite is dur-
ing a partial phase, that is, when the Moon is NOT full. During
partial phases, shadows on the surface 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 surface shadows to yield a pleasing view.
Use the included 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 star diagonal to
attach the Moon filter).
the Planets
The planets don't stay put like the stars (they don't have fixed
R.A. and Dec. coordinates), so you'll have to refer to charts
published monthly in Astronomy, Sky & Telescope, or other
astronomy magazines to locate them. Venus, Mars, Jupiter,
and Saturn are the brightest objects in the sky after the Sun
and the Moon. Not all four of these planets are normally visi-
ble at any one time.
JUPITER The largest planet, Jupiter, is a great subject to
observe. You can see the disk of the giant planet and watch
the ever-changing positions of its four largest moons, Io,
Callisto, Europa, and Ganymede. If atmospheric conditions
are good, you may be able to resolve thin cloud bands on the
planet's disk.
SATURN The ringed planet is a breathtaking sight when it is
well positioned. The tilt angle of the rings varies over a period
of many years; sometimes 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 see-
ing) is necessary for a good view. You may probably see a tiny,
bright "star" close by; that's Saturn's brightest 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 some-
times 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 If atmospheric conditions are good, you may be able
to see some subtle surface detail on the Red Planet, possibly
even the polar ice cap. Mars makes a close approach to Earth
every two years; during those approaches its disk is larger
and thus more favorable for viewing.
Stars
Stars will appear like twinkling points of light in the telescope.
Even powerful telescopes cannot magnify stars to appear as
more than points of light! You can, however, enjoy the different
colors of the stars and locate many pretty double and multiple
stars. The famous "Double-Double" in the constellation Lyra
and the gorgeous two-color double star Albireo in Cygnus are
favorites. Defocusing the image of a star slightly can help
bring out its color.
Deep-Sky Objects
Under dark skies, you can observe a wealth of fascinating
deep-sky objects, including gaseous nebulas, open and
globular star clusters, and different types of galaxies. Most
deep-sky objects are very faint, so it is important that you find
an observing site well away from light pollution. Take plenty of
time to let your eyes adjust to the darkness. Don't expect
these subjects to appear like the photographs you see in
books and magazines; most will look like dim gray smudges.
(Our eyes are not sensitive enough to see color in such faint
objects.) But as you become more experienced and your
observing skills get sharper, you will be able to discern more
subtle details.
Remember that the higher the magnification you use, the dim-
mer the image will appear. So stick with low power when
observing deep-sky objects, because they're already very faint.
Consult a star atlas or observing guide for information on finding
and identifying deep-sky objects. Some good sources to start
with are the Orion DeepMap 600, Edmund Mag 6 Star Atlas,
Turn Left at Orion, and The Universe From Your Backyard.

7. terrestrial Viewing

The SkyView Deluxe 90mm Refractor may also be used for
long-distance viewing over land. For this application we rec-
ommend substitution of an Orion 45° Correct-Image Diagonal
(#8790) for the 90° star diagonal that comes standard with the
telescope. The correct-image diagonal will yield an upright,
non-reversed image and also provides a more comfortable
viewing angle, since the telescope will be aimed more hori-
zontally for terrestrial subjects.
For terrestrial viewing, it's best to stick with low powers of 50x
or less. At higher powers the image loses sharpness and clar-
ity. That's because when the scope is pointed near the
horizon, it is peering through the thickest and most turbulent
part of the Earth's atmosphere.
Remember to aim well clear of the Sun, unless the front
of the telescope is fitted with a professionally made solar
filter and the finder scope is covered with foil or some
other completely opaque material.
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