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TRUE POLE ALIGNMENT of an
OBSERVATORY CLASS EQUATORIAL

5)

Elevate Hour Axis to the True Pole & Zero Dec. Verniers

i) Select an equatorial star near culmination.

ii) With the telescope circle following read the instrumental declination and correct for astronomical refraction.

iii) With the telescope circle preceding repeat.

iv) Half the sum of the dec. readings equals the true instrument dec.

v) Apply the correction by subtracting the true instrument dec. from the apparent dec. given in the ephemeris precessed to epoch of date, and adjusting the elevation of
the pole end of the hour axis in the opposite direction.

vi) Half the difference of the instrument dec. readings equals the dec. vernier error.

vii) Adjust the telescope in dec. by the error, in the opposite direction, and adjust the verniers to read the apparent dec. at epoch of date corrected for refraction.

viii) Repeat & note the elevation error & vernier errors.