Orion OBSERVER 70MM AZ - Manual (Page 13)

tend to scatter light, which reduces an object’s brightness.
Trans parency 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 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 “dip-
per”. If you cannot see Megrez, then you have fog, haze,
clouds, smog, or other conditions that are hindering your
viewing (Figure 8).
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 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
continuously adjusted over time to keep an object in the field
of view. When viewing the with the Observer 70, you will need
to give the optical tube (1) a light tug or push in azimuth (left
or right) as well as an occasional turn of the altitude micro-
motion thumbwheel (13) to keep the object in the field of view.
Make certain the azimuth lock knob (20) is slightly loosened
before moving the scope in azimuth. 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 azimuth, the object will move in the opposite direction in the
eyepiece. This takes some getting used to, but becomes sec-
ond nature after a few nights out with the telescope.
Eyepiece selection
By using eyepieces of different focal lengths, it is possible to
attain many magnifications or powers with the Observer 70.
Your telescope comes with two Explorer II eyepieces
(Figure 9): a 25mm, which gives a magnification of 28x, and a
10mm, which gives a magnification of 70x. 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.
13
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 pre-
serve 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.
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.
Figure 9. The 25mm and 10mm Explorer II eyepieces.