Orion SKYQUEST XT12 User Manual download pdf (Page 16)

common sense prevails. It is especially important that the

optical tube does not get knocked around; this can cause the

optics to become misaligned, and could dent the tube. We

recommend transporting and storing the tube assembly in an

optional padded case for proper protection.

5. Astronomical Observing

The SkyQuest XT12 IntelliScope provides prodigious capa-

bility for observing the many wonders of the heavens, from

the major planets to deep-space nebulas and galaxies. In this

section we give you some observing tips and briefly summa-

rize what you can expect to see.

A. Selecting an Observing Site

Since most astronomical objects are faint, observing them

from dark skies will give you the best views. While some

objects, such as the planets and Moon, are bright enough

to see clearly even from light-polluted city skies, for nebulas,

galaxies, and most star clusters, the less ambient light there

is to reduce contrast, the better.

When it isn’t possible or convenient to get out of town to a

pitch-black observing location, try to set up in a spot that is

removed from street and building lights and that has a clear

view of a large portion of the sky. For observing faint deep-

sky objects, choose a moonless night. Use of a light-pollution

filter can mitigate the effects of background sky brightness,

enhancing the view of faint objects.

B. Seeing and Transparency

Atmospheric conditions play a huge part in quality of viewing.

Light from stars and other celestial objects must travel through

miles of Earth’s atmosphere to reach our eyes. The air in the

atmosphere will refract and bend the light. Atmospheric tur-

bulence will worsen the effects of refraction, which can cause

the image you see in your telescope to be unstable. The

steadiness of the atmosphere is called “seeing.”

In conditions of good “seeing,” star twinkling is minimal and

objects appear steady in the eyepiece. Seeing is best over-

head, worst at the horizon. Also, seeing generally gets better

later in the evening as much of the heat absorbed by the

Earth during the day has radiated off into space. In condi-

tions of bad seeing, stars will twinkle and objects will appear

unsteady and blurry in the telescope.

“Transparency” is the clarity of the atmosphere, which can

be adversely affected by the presence of moisture, smoke,

and dust. All tend to scatter light, which reduces an object’s

brightness. Good transparency is desirable for astronomical

observing, especially for viewing faint objects.

One good measure of transparency is by how many stars

you can see with your unaided eyes. If you cannot see

stars of magnitude 3.5 or dimmer then transparency is poor.

Magnitude is a measure of how bright a star is. The brighter

a star, the lower its magnitude. A good star to remember for

this is Megrez (magnitude 3.4), which is the star in the Big

Dipper that connects the handle to the “dipper.” If you cannot

see Megrez, then you have fog, haze, clouds, smog, light pol-

lution or other conditions that are hindering your viewing (see

Figure 31).

C. Cooling the Telescope

All optical instruments need time to reach “thermal equilibrium”

to achieve maximum stability of the lenses and mirrors, which

is essential for peak performance. Images will be unstable if

the optics are not in equilibrium with the outdoor temperature.

When moved from a warm indoor location outside to cooler

air (or vice-versa), a telescope needs time to cool to the out-

door temperature. The bigger the instrument and the larger

the temperature change, the more time will be needed.

Allow at least 30 minutes for your telescope to equilibrate. If

the temperature difference between indoors and outdoors is

more than 40°, allow an hour or more. In the winter, storing

the telescope outdoors in a shed or garage greatly reduces

the amount of time needed for the optics to stabilize. It also is

a good idea to keep the telescope covered until the Sun sets

so the tube does not heat greatly above the temperature of

the outside air.

The SkyQuest XT12 IntelliScope is designed to accept an

optional Cooling Accelerator Fan. When attached to the rear

cell of the telescope, the fan hastens the equilibration of the

primary mirror to ambient temperature.

D. Let Your Eyes Dark-Adapt

Do not 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. Many observers

notice improvements after several hours of total darkness. As

your eyes become dark-adapted, more stars will glimmer into

view and you will be able to see fainter details in objects you

view in your telescope. Exposing your eyes to very bright day-

light for extended periods of time can adversely affect your

night vision for days. So give yourself at least a little while to

get used to the dark before you begin observing.

To see what you are 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

Figure 31. Megrez connects the Big Dipper’s handle to it’s “pan”.

It is a good guide to judging the “seeing” conditions. If you cannot see

Megrez (a 3.4-magnitude star) then transparency is poor.

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