Orion 9005 Tracking Celestial Objects, Optional Motor Drive, Understanding the Setting Circles

loosen the big tripod attachment knob directly underneath the base of the equatorial mount. The fine adjustment knobs work by loosening one and then tightening the other. When done, retighten the tripod attachment knob to firmly secure the mount and tripod.

Once Polaris is centered in the small circle, you are done. The telescope is now accurately polar aligned, and can be used for advanced observational applications, such as astropho- tography or precise use of the manual setting circles. As mentioned before, only move the telescope along the R.A. and Dec. axes; if you move the tripod, or change the tilt of the equatorial mount, you will need to polar align again.

Remember, accurate polar alignment is not needed for casual visual observing. Most of the time, approximate polar alignment, as outlined previously, will suffice.

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 Drive

An optional DC motor drive system can be mounted on the AstroView’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 system 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 astronomi- cal 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 lines in between representing 10-min- ute increments. The upper set of numbers apply to viewing in the Northern Hemisphere, while the numbers below them apply to viewing in the Southern Hemisphere. The Dec. set- ting circle is scaled in degrees.

Before you can use the setting circles to locate objects, the mount must be accurately polar aligned, and the setting cir- cles must be calibrated. The declination setting circle was calibrated at the factory, and should read 90° when the tele- scope optical tube is pointing exactly along the R.A. 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 levers on the equatorial mount, so the telescope optical tube can move freely.

3Point the telescope at the bright star whose coordinates you know. Center the star in the telescope’s eyepiece. Lock the R.A. and Dec. lock levers.

4.Loosen the large thumbscrew just above the R.A. setting circle and rotate the R.A. setting circle so the pointer indi- cates the R.A. coordinate listed for the bright star in the star atlas. Do not retighten the thumbscrew when using the R.A. setting circles for finding objects; the thumbscrew is only needed for polar alignment using the polar axis finder scope.

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 lever and rotate the telescope until the Dec. value from the star atlas matches the reading on the Dec. setting circle. If the telescope is being aimed toward the south and the Dec. setting circle pointer pass- es the 0° indicator, the value on the Dec. setting circle becomes a negative number. Retighten the lock lever.

2.Loosen the R.A. lock lever 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 lever.

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 recalibrated 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 Figure 1 the telescope is pointed north as it would be during polar alignment. The counterweight shaft is oriented down- ward. But it will not look like that when the telescope is pointed in other directions. Let’s say you want to view an object that is directly overhead, at the zenith. How do you do it?

One thing you DO NOT do is make any adjustment to the latitude adjustment T-bolts. That will spoil the mount’s polar alignment. Remember, once the mount is polar aligned, the telescope should be moved only on the R.A. and Dec. axes. To point the scope overhead, first loosen the R.A. lock lever and rotate the telescope on the R.A. axis until the counter-

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