Orion STARBLAST 6/6I - Manual (Page 14)

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seeing affects images at high powers more severely. Planetary
observing may also be poor.
In conditions of good seeing, star twinkling is minimal and
images appear steady in the eyepiece. Seeing is best over-
head, worst at the horizon. Also, seeing generally gets better
after midnight, when much of the heat absorbed by the Earth
during the day has radiated off into space.
Especially important for observing faint objects is good “trans-
parency” – air free of moisture, smoke, and dust. All tend to scat-
ter light, which reduces an object’s brightness. Transparency is
judged by the magnitude of the faintest stars you can see with
the unaided eye (6th magnitude or fainter is desirable).
If you cannot see stars of magnitude 3.5 or dimmer, then con-
ditions are poor. Magnitude is a measure of how bright a star
is: the brighter the star, the lower its magnitude. A good star
to remember for this is Megrez (mag. 3.4), which is the star in
the “Big Dipper” that connects the “handle” to the “pan” of the
dipper (
Figure 20). If you cannot see Megrez, then you have
fog, haze, clouds, smog, or other conditions (such as light pol-
lution) that are hindering your viewing.
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 see it at night from
the apparent movement of stars from east to west.
When you observe any astronomical object, you are in essence
watching a moving target. This means the telescope’s position
must be continuously adjusted over time to keep the object
in the field of view. This is easy to do with the StarBlast 6/6i
because of its smooth motions on both axes. As the object
moves off towards the edge of the field of view, just lightly
nudge the telescope to re-center it.
Objects appear to move across the field of view faster at high-
er magnifications. This is because the field of view becomes
narrower.
Eyepiece Selection
By using eyepieces of different focal lengths, it is possible to
attain many magnifications, or powers, with the StarBlast 6/6i.
Your telescope comes with two Sirius Plössl eyepieces of dif-
ferent focal lengths: a 25mm, which provides a magnification
of 30x, and a 10mm, which yields 75x. Other eyepieces can be
used to achieve higher or lower powers. It is quite common for
an observer to own many eyepieces to access a wide range of
magnifications.
To calculate the magnification of a telescope-eyepiece com-
bination, simply divide the focal length of the telescope by the
focal length of the eyepiece.
Telescope Focal Length (mm)
= Magnification
Eyepiece Focal Length (mm)
For example, the StarBlast 6, which has a focal length of
750mm, used in combination with the 25mm eyepiece, yields
a magnification of
750mm
= 30x
25mm
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
finding and centering an object much easier. Trying to find and
center objects with a high-power (narrow field of view) eye-
piece is like trying to find a needle in a haystack!
Once you’ve centered the object in the eyepiece, you can
switch to a higher magnification (shorter focal length) eye-
piece, if you wish. This is recommended for small and bright
objects, like planets and double stars. The Moon also takes
higher magnifications well.
The best rule of thumb with eyepiece selection is to start with
a low-power, wide-field eyepiece, and then work your way up
in magnification. If the object looks better, try an even higher
magnification eyepiece. If the object looks worse, then back off
the magnification a little by using a lower-power eyepiece.
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, phases of Venus, and many bright deep-sky objects. Do
not expect to see 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 faint
deep-sky objects, except in a few of the brightest ones.
Remember that you are seeing these objects with your own
eyes in real time, using your own telescope! That beats looking
at a picture in a book or on a computer screen, in our opinion.
Each session with your telescope will be a learning experi-
ence. Each time you work with your telescope it will get easier
to use, and celestial objects will become easier to find. There
is a big difference between looking at a well-made, full-color
NASA image of a deep-sky object in a lit room during the day-
time, and seeing that same object in your telescope at night.
Figure 20. Megrez connects the Big Dipper’s “handle” to its
“pan.” If you cannot see Megrez, a magnitude 3.4 star, then
the viewing conditions are poor.