Orion SPACEPROBE 130ST EQ - Manual (Page 12)

may be perfectly aligned. It is critical to keep the star cen-
tered, so over time you will need to make slight corrections
to the telescope’s position in order to account for the sky’s
apparent motion.
7. using Your telescope—
Astronomical Observing
Choosing an Observing Site
When selecting a location for observing, get as far away as
possible from direct artificial light such as street lights, porch
lights, and automobile headlights. The glare from these lights
will greatly impair your dark-adapted night vision. Set up on
a grass or dirt surface, not asphalt, because asphalt radiates
more heat. heat disturbs the surrounding air and degrades
the images seen through the telescope. Avoid viewing over
rooftops and chimneys, as they often have warm air currents
rising from them. Similarly, avoid observing from indoors
through an open (or closed) window, because the tempera-
ture difference between the indoor and outdoor air will cause
image blurring and distortion.
If at all possible, escape the light-polluted city sky and head
for darker country skies. You’ll be amazed at how many more
stars and deep-sky objects are visible in a dark sky!
“Seeing” and transparency
Atmospheric conditions vary significantly from night to night.
“Seeing” refers to the steadiness of the Earth’s atmosphere
at a given time. In conditions of poor seeing, atmospheric
turbulence causes objects viewed through the telescope to
“boil”. If, when you look up at the sky with just your eyes, the
stars are twinkling noticeably, the seeing is bad and you will
be limited to viewing with low powers (bad 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
“transparency”— air free of moisture, smoke, and dust. All
tend to scatter 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).
Cooling the telescope
All optical instruments need time to reach “thermal equilib-
rium”. The bigger the instrument and the larger the tempera-
ture change, the more time is needed. Allow at least 30 min-
utes for your telescope to cool to the temperature outdoors.
In very cold climates (below freezing), it is essential to store
the telescope as cold as possible. If it has to adjust to more
than a 40° temperature change, allow at least one hour.
let Your Eyes Dark-Adapt
Don’t expect to go from a lighted house into the darkness
of the outdoors at night and immediately see faint nebulas,
galaxies, and star clusters—or even very many stars, for
that matter. Your eyes take about 30 minutes to reach per-
haps 80% of their full dark-adapted sensitivity. As your eyes
become dark-adapted, more stars will glimmer into view and
you’ll be able to see fainter details in objects you view in your
telescope.
To see what you’re doing in the darkness, use a red-filtered
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 incandescent flashlight with red cellophane or paper.
Beware, too, that nearby porch and streetlights and car
headlights will ruin your night vision.
Eyepiece Selection
By using eyepieces of varying focal lengths, it is possible to
attain many magnifications with the SpaceProbe 130ST EQ.
The telescope comes with two high-quality Sirius Plössl eye-
pieces: a 25mm, which gives a magnification of 26x, and a
10mm, which gives a magnification of 65x. 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.
To calculate the magnification, or power, of a telescope and
eyepiece combination, simply divide the focal length of the
telescope by the focal length of the eyepiece:
focal length of telescope
Magnification =
focal length of eyepiece
For example, the SpaceProbe 130ST EQ, which has a focal
length of 650mm, used in combination with the 25mm eye-
piece, yields a magnification of
650mm = 26x
25mm
12
Figure 12. A star test will determine if a telescope’s optics are
properly collimated. An unfocused view of a bright star through the
eyepiece should appear as illustrated on right if optics are perfectly
collimated. If circle is unsymmetrical, as in illustration on left, scope
needs collimation.
Out of collimation Collimated