Orion 9025, 9086 Tracking Celestial Objects, Understanding the Setting Circles, R.A. 5h 35.4m Dec

scale is set at the latitude of your observing site. If you don’t know your latitude, consult a geographical atlas to find it. For example, if your latitude is 35° North, set the pointer to +35. Then retighten the latitude locking t-bolt. The latitude setting should not have to be adjusted again unless you move to a different viewing location some dis- tance away.

3.Loosen the Dec. lock knob and rotate the telescope opti- cal tube until it is parallel with the R.A. axis. The pointer on the Dec. setting circle should read 90°. Retighten the Dec. lock knob.

4.Loosen the azimuth adjustment knob and rotate the entire equatorial mount left-to-right so the telescope tube (and R.A. axis) points roughly at Polaris. If you cannot see Polaris directly from your observing site, consult a com- pass and rotate the equatorial mount so the telescope points North. Retighten the azimuth adjustment knob.

The equatorial mount is now approximately polar-aligned for casual observing. More precise polar alignment is required for astrophotography. Several methods exist and are described in many amateur astronomy reference books and astronomy magazines.

Note: From this point on in your observing session, you should not make any further adjustments in the azimuth or the latitude of the mount, nor should you move the tri- pod. Doing so will undo the polar alignment.The telescope should be moved only about its R.A. and Dec. axes.

Tracking Celestial Objects

When you observe a celestial object through the telescope, you’ll see it drift slowly across the field of view. To keep it in the field, if your equatorial mount is polar-aligned, just turn the R.A. slow-motion control. The Dec. slow-motion control is not needed for tracking. Objects will appear to move faster at higher magnifications, because the field of view is narrower.

Optional Motor Drives for Automatic Tracking and Astrophotography

An optional DC motor drive (#7827) can be mounted on the R.A. axis of the Skywatcher’s equatorial mount to provide hands-free tracking. Objects will then remain stationary in the field of view without any manual adjustment of the R.A. slow- motion control. The motor drive is necessary for astrophotography.

Understanding the Setting Circles

The setting circles on an equatorial mount enable you to locate celestial objects by their “celestial coordinates.” Every astronomical object resides in a specific location on the “celestial sphere.” That location is denoted by two numbers: its right ascension (R.A.) and declination (Dec.). In the same way, every location on Earth can be described by its longitude and latitude. R.A. is similar to longitude on Earth, and Dec. is similar to latitude. The R.A. and Dec. values for celestial objects can be found in any star atlas or star catalog.

So, the coordinates for the Orion Nebula listed in a star atlas will look like this:

R.A. 5h 35.4m Dec. -5° 27'

That’s 5 hours and 35.4 minutes in right ascension, and -5 degrees and 27 arc-minutes in declination (the negative sign denotes south of the celestial equator). There are 60 minutes in 1 hour of R.A. and there are 60 arc-minutes in 1 degree of declination.

The telescope’s R.A. setting circle is scaled in hours, from 1 through 24, with small hash marks in between representing 10-minute increments. The lower set of numbers (closest to the plastic R.A. gear cover) apply to viewing in the Northern Hemisphere, while the numbers above them apply to viewing in the Southern Hemisphere. The Dec. setting circle is scaled in degrees.

Before you can use the setting circles to locate objects, the mount must be polar aligned, and the setting circles must be calibrated. The declination setting circle was calibrated at the factory, and should read 90° when the telescope optical tube is pointing exactly along the polar axis.

Calibrating the Right Ascension Setting Circle

1.Identify a bright star near the celestial equator and look up its coordinates in a star atlas.

2.Loosen the R.A. and Dec. lock knobs on the equatorial mount, so the telescope optical tube can move freely.

3.Point the telescope at the bright star near the celestial equa- tor whose coordinates you know. Center the star in the telescope’s field of view. Lock the R.A. and Dec. lock knobs.

4.Rotate the R.A. setting circle so the pointer indicates the R.A. listed for the bright star in the star atlas.

Finding Objects With the Setting Circles

Now that both setting circles are calibrated, look up in a star atlas the coordinates of an object you wish to view.

1.Loosen the Dec. lock knob and rotate the telescope until the Dec. value from the star atlas matches the reading on the Dec. setting circle. Retighten the lock knob. Note: If the telescope is aimed south and the Dec. setting circle point- er passes the 0° indicator, the value on the Dec. setting circle becomes a negative number.

2.Loosen the R.A. lock knob and rotate the telescope until the R.A. value from the star atlas matches the reading on the R.A. setting circle. Retighten the lock knob.

Most setting circles are not accurate enough to put an object dead-center in your finder scope’s field of view, but they’ll get you close, assuming the equatorial mount is accurately polar- aligned. The R.A. setting circle should be re-calibrated every time you wish to locate a new object. Do so by calibrating the setting circle for the centered object before moving on to the next one.

Confused About Pointing the Telescope?

Beginners occasionally experience some confusion about how to point the telescope overhead or in other directions. In

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