7
Choosing an Observing Site
When selecting a location for observing, get as far away as pos-
sible from direct artificial light such as street lights, porch lights,
and automobile headlights. The glare from these lights will great-
ly 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) win-
dow, because the temperature 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 turbu-
lence causes objects viewed through the telescope to “boil.”
If you look up at the sky and stars are twinkling noticeably,
the seeing is poor and you will be limited to viewing at lower
magnifications. At higher magnifications, images will not focus
clearly. Fine details on the planets and Moon will likely not be
visible.
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 (5th or 6th magnitude is desirable).
Cooling the Telescope
All optical instruments need time to reach “thermal equilibri-
um.” The bigger the instrument and the larger the temperature
change, the more time is needed. Allow at least 30 minutes for
your telescope to acclimate to the temperature outdoors before
you start observing with it.
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 perhaps 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 flash-
light 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. Beware, too, that nearby porch, streetlights, and car
headlights will ruin your night vision.
Figure 10
.
Secure the star diagonal in the focuser drawtube with
the thumbscrew on the drawtube collar, then install the eyepiece in
the diagonal.
Eyepiece
Thumbscrew
Thumbscrew Focus wheel
Focuser
drawtube
Star diagonal
Figure 11.
The red dot finder scope has vertical and (inset)
horizontal adjustment knobs for aligning it with the telescope.
Power switch
Plastic
tab
Vertical knob
Horizontal knob
Opposite side
Figure 12
. The micro-motion rod and thumbwheel allow fine
altitude pointing control.
Thumbwheel
Micro-motion rod
Yoke knob
Altitude lock
knob
