North Celestial Pole
(near Polaris)
Declination
Circle
Polar axis
Right Latitude
Ascension
Circle
Movement for altitude adjustment
Figure 1
Movement for
Polar axis alignment
(precise setting)
The following process will allow tracking without the need for occasional corrections, and is essential if photography using a motorised drive is envisioned. If the approx- imate alignment described above has been carried out correctly, only very minor adjust- ments in azimuth
Polar axis elevation
(altitude) alignment
Choose a bright star in the east and locate in the eyepiece field. Establish the current axial motion of the telescope by gently moving the telescope tube back and forth, (rotating east-
Polar axis
Rotation for
Figure 2
west on the polar axis only as shown in figure 2a) so that the star is impelled to move from one side of the eyepiece field to the other. It will help if you arrange this line of motion to bisect the eyepiece field (as in figure 2b ).
This procedure can be made easier if a reticle is placed at the eyepiece focus and aligned to indicate this motion, rather than having to remember it in the mind's eye.
The reticle can be a rolled piece of cardboard, joined by sticky tape, of such a diameter that it snugly fits into the inner barrel of the eye- piece. A hair or thread is fastened across one end of this cardboard tube, approximately bisecting it (figure 3a ). A cross hair reticle may already be supplied with your instrument (figure 3b ).
hair or thread
Figure 3
Holding the eyepiece up to the light, it should be possible to insert the reticle until the fila- ment comes into focus. (Note. The insertion of a reticle is only possible with certain eyepiece designs.) The filament, or one of the cross hairs, can then be aligned (by turning the eyepiece) to establish the direction of axial movement as required (as in figure 4).
a | stars motion | b |
| reticle |
| line |
| (aligned to |
Figure 4 | axial motion) |
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