Simplified method (based on idea by E.S. King)
The precise alignment needs some knowledge and the detailed acquaintance with each practical step. In order that the advantages are quickly visible I present a simplified version which does not deliver high accuracy but emphasizes the principle points.
Approximate leveling of the tripod. It is sufficient to to that carefully by the eye.
Rough alignment with the help of the pole finder telescope. If there is no pole finder use the the main telescope in the same manner.
Calibration of the measurement field of the eyepiece. In the simplest form this eyepiece should have a reticle with intersections better is a a quadratic grid. The field of view de can be calculated in arc seconds with the simplified equation
with a star in the vicinity (
< ±10o) of the celestial equator. The
diameter of the field of view should not exceed 300...400 ''. If
there are intersections then divide the diameter by the number of
units and this is the unit of the grid in arc seconds.
Center Polaris with running tracking motors.
After an eventually recentering Polaris let the telescope track this star without any intervention for 1371 seconds or about 23 minutes.
Estimate now the Polaris' path l in arc seconds and calculate with the equation
the polar distance of the hour axis. This result gives a good impression about the accuracy of the alignment. Despite all simplifications this value is accurate within the error of the measurement.
Make a sketch to scale of the measurement field and the observed path of Polaris in the eyepiece. Turn this diagram by 90o clockwise. The resulting direction of the path is the direction in which you have to move the hour axis. The new horizontal component of the path is directly the azimuthal length of the correction and the perpendicular that of the elevation.
If you project the end point of Polaris' path on the two axes and multiply this value by a factor of 10 then you receive the length in arc seconds of the corrections in both directions.
Center Polaris again and move the hour axis in that direction by the calculated amount. Finally you will get closer and closer to the apparent (refracted) pole.
Check the resulting alignment by working through points 1 to 7. Is the length of the path in point 7 shorter and hence the polar distance smaller then the basic task is accomplished. In case where the path is longer check points 3 and 8.
I would like to emphasize again that this simplified version does not provide accurate alignment and that it is only important that the polar distance decreases.
Comments, questions, corrections: markus.wildi@one-arcsec.org