Celestial Observing • 45
Deep-sky objects are simply those objects outside the boundaries of our solar
system. They include star clusters, planetary nebulae, diffuse nebulae, double
stars, and other galaxies outside our own Milky Way. The Celestron Sky
Maps (#93722) can help you locate the brightest deep-sky objects. You can
use your setting circles or “star hop” to an object from an area with which you
are familiar.
Most deep-sky objects have a large angular size. Therefore, low-to-moderate
power is all you need to see them. Visually, they are too faint to reveal any
color seen in long exposure photographs. Instead, they have a black and white
appearance. And, because of their low surface brightness, they should be
observed from a dark sky location. Light pollution around large urban areas
washes out most nebulae making them difficult, if not impossible, to observe.
Light Pollution Reduction filters help reduce the background sky increasing
contrast.
Using Your Setting Circles
Once the setting circles are aligned you can use them to find any object with
known coordinates.
1.
Select an object to observe. Use a seasonal star chart or planisphere to
make sure the object you chose is above the horizon. As you become
more familiar with the night sky, this will no longer be necessary.
2.
Look up the coordinates in an atlas or reference book.
3.
Move the telescope in declination until the indicator is pointing at the
correct declination coordinate.
4.
Move the telescope in R.A. until the indicator points to the correct coordi-
nate (do NOT move the R.A. circle). The telescope will track in R.A. as
long as the clock drive is operating.
5.
Look through the finder to see if you have located the object.
6.
Center the object in the finder.
7.
Look in the main optics using a low power eyepiece; the object should be
there.
8.
Repeat the process for each object observed throughout the observing
session.
You may not be able to see fainter objects in the finder. When this happens,
gradually sweep the telescope around until the object is visible.
The declination setting circle is scaled in degrees while the R.A. setting circle
is incremented in minutes with a marker every five minutes (see figure 6-2). As
a result, the setting circles will get you close to your target, but not directly on
it. Also, the accuracy of your polar alignment will also affect how accurately
your setting circles read. It should be noted that the R.A. setting circle does
not remain calibrated when using any of the slewing rates.
At the end of this manual there is a list of deep-sky objects well within reach of
your Celestron CM-1100 telescope.
Observing Deep-Sky
Objects
Figure 6-2
The R.A. setting circle (top) and
the DEC circle (bottom).
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70
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