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Figure 7.
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.
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
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).
One good way to tell if conditions are good is by how many
stars you can see with your naked eye. If you cannot see stars
of magnitude 3.5 or dimmer then conditions 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 remem-
ber 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 (Figure 7).
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 cool to the temperature outdoors.
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, gal-
axies, 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 tele-
scope.
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 head-
lights will ruin your night vision.
Eyepiece selection
By using eyepieces of varying focal lengths, it is possible to
attain many magnifications with the Transporter 70 Min-EQ.
Your telescope comes with two Explorer II eyepieces, a 17mm
that gives a magnification of 21x, and a 6mm that gives a
magnification of 58x. 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 magni-
fications. 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
focal length of eyepiece
For example, the Transporter 70 Min-EQ, which has a focal
length of 350mm, used in combination with the 17mm eye-
piece, yields a magnification of:
350mm
Every telescope has a useful magnification limit of about 2x
per millimeter of aperture (which means maximum magnifica-
tion of about 140x for the Transporter 70 Min-EQ). Claims of
higher power by some telescope manufacturers are a mis-
leading advertising gimmick and should be dismissed. Keep in
mind that at higher powers, an image will always be dimmer
and less sharp (this is a fundamental law of optics). The
steadiness of the air (the "seeing") can also limit how much
magnification an image can tolerate.
Whatever you choose to view, always start by inserting your
lowest-power (longest focal length) eyepiece to locate and
center the object. Low magnification yields a wide field of view,
which shows a larger area of sky in the eyepiece. This makes
acquiring and centering an object much easier. If you try to
find and center objects with high power (narrow field of view),
it's like trying to find a needle in a haystack! Once you've cen-
tered the object in the eyepiece, you can switch to higher
magnification (shorter focal length eyepiece), if you wish.
The best rule of thumb with eyepiece selection is to start with
a low power, wide-field eyepiece, and then work your way up
in magnification. If the object looks better, try an even higher
magnification. If the object looks worse, then back off the mag-
nification a little by using a lower-power eyepiece.
What to Expect
So what will you see with your telescope? You should be able
to see bands on Jupiter, the rings of Saturn, craters on the
Moon, the waxing and waning of Venus, and many bright
deep-sky objects. Do not expect to see color as you do in
NASA photos, since those are taken with long-exposure cam-
eras and have "false color" added. Our eyes are not sensitive
enough to see color in deep-sky objects except in a few of the
brightest ones.
= Magnification
= 21x
17mm
9
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