Celestron CGEM DX, Instruction Manual

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19
The constant, mentioned above, is a relationship between your
latitude and the angular distance the celestial pole is above the
northern (or southern) horizon; The angular distance from the
northern horizon to the north celestial pole is always equal to
your latitude . To illustrate this, imagine that you are standing
on the north pole, la90° . The north celestial pole, which
has a declination of +90°, would be directly overhead (i .e ., 90
above the horizon) . Now, let’s say that you move one degree
south — your latitude is now +89° and the celestial pole is
no longer directly overhead . It has moved one degree closer
toward the northern horizon . This means the pole is now 89°
above the northern horizon . If you move one degree further
south, the same thing happens again . You would have to travel
70 miles north or south to change your latitude by one degree .
As you can see from this example, the distance from the
northern horizon to the celestial pole is always equal to
your latitude .
If you are observing from Los Angeles, which has a latitude of
34°, then the celestial pole is 34° above the northern horizon .
All a latitude scale does then is to point the polar axis of
the telescope at the right elevation above the northern (or
southern) horizon . To align your telescope:
1 . Make sure the polar axis of the mount is pointing due north .
Use a landmark that you know faces north .
2 . Level the tripod . There is a bubble level built into the mount
for this purpose .
3 . Adjust the mount in altitude until the latitude indicator points
to your latitude . Moving the mount affects the angle the
polar axis is pointing . For specific information on adjusting
the equatorial mount, please see the section “ Adjusting
the Mount .”
This method can be done in daylight, thus eliminating the
need to fumble around in the dark . Although this method does
NOT put you directly on the pole, it will limit the number of
corrections you will make when tracking an object . It will also
be accurate enough for short exposure prime focus planetary
photography (a couple of seconds) and short exposure
piggyback astrophotography (a couple of minutes) .
All-Star Polar Align
The CGEM DX mount has a polar alignment function
called “All-Star” polar alignment that will help you polar
align your telescope for increased tracking precision and
astrophotography . This feature allows you to choose any bright
alignment star to assist in accurately aligning your telescope’s
mount with the North Celestial Pole . Before using the Polar
Align feature, the scope must first be roughly pointed towards
North and should be aligned with two stars in the sky . See
the “ Latitude Scale ” section for help with finding north and
adjusting the mounts latitude .
Once your telescope is aligned on two stars and at least one
additional calibration star, slew the telescope to any bright star
in its Named Star database list . For best results choose a polar
alignment star that is high in the sky and near the Meridian . Try
to avoid stars that are close to the west/east horizon, directly
overhead or too near the celestial pole . Once there, press
the Align button and use the Up/Down buttons on the hand
controller to select Polar Align from the list .
The Polar Align feature has two options:
Align Mount — After performing a two star alignment and
slewing your telescope to any bright star in the telescope’s
database, select the “Align Mount” option . The telescope will
then re-slew to the same star .
1 . Center the star in the finderscope and press ENTER .
2 . Then accurately center the star in your eyepiece and press
ALIGN . The telescope will then “sync” on this star and slew
to the position that the star should be if it were accurately
polar aligned .
For the most accurate alignment it is best to use a reticle
eyepiece (see Optional Accessories ) or a high power eyepiece
to precisely center the star in the field of view .
3 . Use the mounts latitude and azimuth adjustments (see figure
2-10) to place the star in the center of the eyepiece . Do not
use the direction buttons on the hand control to position
the star
. Once the star is centered in the eyepiece, press
ENTER; the polar axis should now be pointed towards the
North Celestial Pole .
Updating your Star Alignment
After polar alignment it’s a good idea to check the pointing
accuracy of the telescope to see how much it may have been
affected by moving the mount . Since the polar alignment
process requires you to “sync” the telescope on a bright star
before you begin, it will be necessary to undo the sync before
re-aligning . To undo the sync:
1 . Press the
Align button and use the Up/Down buttons on the
hand controller to select Undo Sync from the list, and press
Enter . The message Complete will display on the LCD .
To re-align your telescope:
2 . Slew the telescope to one of the original alignment stars,
or another bright star if the original alignment stars are no
longer in a convenient location . Press the Align button and
use the Up/Down buttons on the hand controller to select
Alignment Stars from the list .
3 . The hand control will ask you which of the original alignment
stars you wish to replace . Use the Up/Down buttons to select
the desired star and press Enter .
4 . Once again center the star in the finderscope and
press Enter .
5 . Then center the star in the eyepiece and press Align .
6 . Repeat the process on a second alignment star .
For additional all sky pointing accuracy, it’s a good idea to
align on at least one additional calibration star located on the
opposite side of the Meridian . To add calibration stars:
1 . Slew the telescope to a bright star on the opposite of the
Meridian from your two alignment stars .
2 . Press the Align button and use the Up/Down buttons on the
hand controller to select Calib . Stars from the list, and
press Enter .
3 . Align the star in the finderscope and then the eyepiece as
you did with the alignment stars .
Display Align — the user can now display the polar alignment
error in the RA and DEC axes . These values show how close
the mount is pointed at the celestial pole base on how
accurately the user centered the alignment star with the
hand control and with the mount adjustment . To display the
alignment error:
1 . Press the
Align button and use the Up/Down buttons on
the hand controller to select Display Align from the list, and
press Enter .
Pointing at Polaris
This method of Polar aligning utilizes Polaris as a guidepost
to the celestial pole . Since Polaris is less than a degree from