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TRUE POLE ALIGNMENT of an
OBSERVATORY CLASS EQUATORIAL


Method Summary

i) Measure dec. drift and determine hourly rate.

ii) Read off the theoretical rate at the mean dec. and hour angle.

iii) Subtract the observed rate.

iv) Read off the corresponding value of gamma at the mean hour angle.

IMAGE imgs/TRUE_POLE_ALIGNMENT13.jpg

v) Apply correction in opposite direction to error.

IMAGE imgs/TRUE_POLE_ALIGNMENT14.jpg

Arefinement of this method which can accommodate azimuth misalignments is described by W.R. Vezin, 'Polar Axis Alignment of Equatorial Instruments,' J.B.A.A.
1978, 88, 3, p267.

Conclusion

It should be manifestly obvious that trial & error alignment methods intended to minimise dec. drift are both inappropriate & meaningless. It is not possible to adjust the
hour axis to counteract dec. drift due to refraction at all declinations & hour angles. Any alignment that minimises dec. drift at certain decs. & HA's elevates the hour
axis above the true pole.

For the most precise PA measures of high dec. pairs, the hour axis MUST be elevated to the true pole. This may ONLY be accomplished by employing a TRUE POLE
alignment method. I therefore strongly recommend that all those with alignments that minimise dec. drift realign their equatorials using the method outlined. Dec. drift
should not effect your measures if made at culmination.