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TRUE POLE ALIGNMENT of an
OBSERVATORY CLASS EQUATORIAL

4)

Square Dec. Axis to Hour Axis

i) Most instruments have no facility for correcting this error.

ii) Align the telescope on a polar star

IMAGE imgs/TRUE_POLE_ALIGNMENT02.jpg


iii) With the telescope circle preceding note the hour angle and sidereal time.

iv) Reverse the telescope circle following and repeat.

v) If angle H is less than a right angle, the star's hour angle west will be too great and hour angle east will be too small.

vi) The difference in HA less the sidereal time interval and 12hrs., gives twice the error.

IMAGE imgs/TRUE_POLE_ALIGNMENT03.jpg

vii) Convert the time error to arc and either record it or apply the correction by shimming the dec. axis bearings.

viii) Repeat and note the residual error.