Using Your Telescope; Astronomical Viewing; Astronomical Observing - Orion Observer 60 Instruction Manual

6.using Your telescope ‑

astronomical observing

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, which
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,
when you look up at the sky with your naked 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 pow-
ers more severely). Planetary observing may also be poor.
In conditions of good seeing, star twinkling is minimal and imag-
es appear steady in the eyepiece. Seeing is best overhead, 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 "transpar-
ency" 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).
If you cannot see stars of magnitude 3.5 or dimmer then condi-
tions are poor. Magnitude is a measure of how bright a star is
- the brighter a star is, the lower its magnitude will be. A good star
to remember for this is Megrez (mag. 3.4), which is the star in the
"Big Dipper" connecting the handle to the "dipper". If you cannot
see Megrez, then you have fog, haze, clouds, smog, or other
conditions that are hindering your viewing. (See Figure 8).
tracking celestial objects
The Earth is constantly rotating about its polar axis, completing
one full rotation every 24 hours; this is what defines a "day". We
do not feel the Earth rotating, but we can still tell that it is at night
by seeing the apparent movement of stars from east to west.
When you observe any astronomical object, you are watching a
moving target. This means the telescope's position must be con-
tinuously adjusted over time to keep an object in the field of view.
When viewing the with the Observer 60, you will need to give the
optical tube a light tug or push in azimuth (left or right) as well
as an occasional turn of the altitude micro-motion thumbwheel)
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to keep the object in the field of view. (Make certain the azimuth
lock knob is slightly loosened before moving the scope in the
azimuth position.) Objects will appear to move faster at higher
magnifications because the field of view is narrower.
Remember that objects are reversed left to right in refractor
telescopes, so when you move the telescope in one direction in
the azimuth, the object will move in the opposite direction in the
eyepiece. This takes some getting used to, but becomes second
nature after a few nights out with the telescope.
Figure 8.
Megrez connects the Big Dipper's handle to it's "pan". It is
a good guide to how conditions are. If you can not see Megrez (a 3.4
mag star) then conditions are poor.
light Pollution
Most of us live where city lights interfere with our view
of the heavens. As our metropolitan areas have become
more developed, the scourge of light pollution has
spread, washing out many stars and nonstellar celestial
objects from our sight. Faint deep sky objects become
difficult or impossible to see through the murk of light
pollution. Even bright nebulas like the Orion and Lagoon
Nebulas lose much of their delicate detail. The Moon and
planets are not affected; they require steady air more
than dark skies, so they remain good targets for city-
dwelling observers.
The International Dark-Sky Association is waging the
fight against light pollution. The IDSA was founded in
1988 with the mission of educating the public about
the adverse impact that light pollution has on the night
sky and astronomy. Through educational and scientific
means, the nonprofit IDA works to raise awareness about
the problem and about measures that can be taken to
solve it.
Do you need help dealing with local officials to control
street or building lighting in your area? The IDA's exten-
sive support materials can show you how. Help preserve
dark skies, join the IDA today! For information, write to
IDA, 3225 N. First Ave., Tuscon, AZ 85719-2103 or visit
their website: www.darksky.org.
The best way to avoid immediate problems with light pol-
lution, however, is to take you telescope to where there
are dark skies. You will be amazed at how many stars
you can see when you get away from the city lights.