Celestar Manual
Astronomy Basics
35
To perform the declination drift method you need to choose two bright stars. One should be near the
eastern horizon and one due south near the meridian. Both stars should be near the celestial equator (i.e.,
0° declination). You will monitor the drift of each star one at a time and in declination only. While
monitoring a star on the meridian, any misalignment in the east-west direction is revealed. While
monitoring a star near the east/west horizon, any misalignment in the north-south direction is revealed. As
for hardware, you will need an illuminated reticle ocular to help you recognize any drift. For very close
alignment, a Barlow lens is also recommended since it increases the magnification and reveals any drift
faster.When looking due south, insert the diagonal so the eyepiece points straight up. Insert the cross hair
ocular and align the cross hairs so that one is parallel to the declination axis and the other is parallel to the
right ascension axis. Move your telescope manually in R.A. and DEC to check parallelism.
First, choose your star near where the celestial equator and the meridian meet. The star should be
approximately within 1/2 an hour of the meridian and within five degrees of the celestial equator. Center
the star in the field of your telescope and monitor the drift in declination.
•
If the star drifts south, the polar axis is too far east.
•
If the star drifts north, the polar axis is too far west.
Make the appropriate adjustments to the polar axis to eliminate any drift. Once you have eliminated all the
drift, move to the star near the eastern horizon. The star should be 20 degrees above the horizon and within
five degrees of the celestial equator.
•
If the star drifts south, the polar axis is too low.
•
If the star drifts north, the polar axis is too high.
Again, make the appropriate adjustments to the polar axis to eliminate any drift. Unfortunately, the latter
adjustments interact with the prior adjustments ever so slightly. So, repeat the process again to improve the
accuracy checking both axes for minimal drift. Once the drift has been eliminated, the telescope is very
accurately aligned. You can now do prime focus deep-sky astrophotography for long periods.
NOTE: If the eastern horizon is blocked, you may choose a star near the western horizon, but you must
reverse the polar high/low error directions. Also, if using this method in the southern hemisphere,
the direction of drift is reversed for both R.A. and DEC.
ALIGNING THE RA SETTING CIRCLE
In order to align the R.A. setting circle, you must first polar align the telescope mount. Second, you need
to know the names of a few of the brightest stars in the sky. If you don't, they can be learned by using the
Celestron Sky Maps (#93722) or consulting a current astronomy magazine. To align the R.A. setting
circle:
1.
Locate a bright star near the celestial equator. The farther you are from the celestial pole, the better
your reading of the R.A. setting circle. The star you choose to align the setting circle should be a
bright one whose coordinates are known and easy to look up. (For a list of bright stars to align the
R.A. setting circle, see the list at the back of this manual.)
2.
Center the star in the finder.
3.
Center the star in the field of view of the telescope.
