Observing Deep-Sky Objects

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Figure 6-2

The R.A. setting circle (top) and the DEC circle (bottom).

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.

Celestial Observing • 45