Use of the R.A. and Dec Slow-Motion Control Cables

For example, if it was November 1 at 9 PM, standard time, you would rotate the telescope in R.A. until the line above the “21” (9 P.M.) on the R.A. setting circle lines up with the long line between the “10” and “11” on the date circle. The long line indicates the first day of the higher numbered month, i.e. the line between “10” and “11” marks November 1st.

Finally, look through the polar alignment finder scope while shining a red flashlight at an angle down the front opening of the R.A. axis, and center Polaris in the small circle. Adjust the tilt of the altitude up-or-down with the latitude adjustment T-bolts and use the azimuth fine adjustment knobs (Figure 8) for final positioning. To do this, you will first need to loosen the big tripod attachment knob directly underneath the base of the equatorial mount. The fine adjustment knobs work by loosen- ing one and then tightening the other. Once Polaris is centered in the small circle, retighten the tripod attachment knob to firmly secure the mount and tripod. If the fine adjustment knobs do not allow the mount to move far enough to center Polaris, you will need to rotate the entire tripod left or right to get it within the fine adjustment’s range.

The telescope is now accurately polar aligned, and can be used for advanced observational applications, such as astro- photography 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 align- ment, as outlined previously, will suffice.

Use of the R.A. and Dec.

Slow-Motion Control Cables

The R.A. and Dec. slow-motion control cables allow fine adjustment of the telescope’s position to center objects within the field of view. Before you can use the cables, you must manually “slew” the mount to point the telescope in the vicinity of the desired target. Do this by loosening the R.A. and Dec. lock levers and moving the telescope about the mount’s R.A. and Dec. axes. Once the telescope is pointed somewhere close to the object to be viewed, retighten the mount’s R.A. and Dec. lock levers.

The object should now be visible somewhere in the tele- scope’s finder scope. If it isn’t, use the slow-motion controls to scan the surrounding area of sky. When the object is visible in the finder scope, use the slow-motion controls to center it. Now, look in the telescope’s eyepiece. If the finder scope is properly aligned, the object should be visible somewhere in the field of view. Once the object is visible in the eyepiece, use the slow-motion controls to center it in the field of view.

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 cable clockwise. The Dec. slow- motion control cable 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

An optional DC motor drive can be mounted on the R.A. axis of the 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 cable.

Understanding the Setting Circles

The setting circles on an equatorial mount enable you to locate celestial objects by their “celestial coordinates”. Every 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.

The R.A. setting circle is scaled in hours, from 1 through 24, with small marks in between representing 10-minute incre- ments (there are 60 minutes in 1 hour of R.A.). 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 location of the R.A. coordinate indicator arrow is shown in Figure 3.

The Dec. setting circle is scaled in degrees, with each mark representing 2° increments. Values of Dec. coordinates range from +90° to -90°. The 0° mark indicates the celestial equator. When the telescope is pointed north of the celestial equator, values of the Dec. setting circle are positive; when the tele- scope is pointed south of the celestial equator, values of the Dec. setting circle are negative.

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 (there are 60 arc- minutes in 1 degree of declination).

Before you can use the setting circles to locate objects, the mount must be well polar aligned, and the R.A. setting circle must be calibrated. The Dec. setting circle has been calibrated at the factory, and should read 90° whenever the telescope optical tube is parallel with the R.A. axis.

Calibrating the Right Ascension Setting Circle

1.Identify a bright star in the sky near the celestial equator (Dec. = 0°) 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.

3.Point the telescope at the bright star whose coordinates you know. Lock the R.A. and Dec. lock levers. Center the star in the telescope’s field of view with the slow-motion control cables.

4.Loosen the R.A. setting circle lock thumbscrew (see Figure 3); this will allow the setting circle to rotate freely. Rotate the setting circle until the arrow under the thumbscrew indicates the R.A. coordinate listed in the star atlas for the object. Do not retighten the thumbscrew when using the R.A. setting