Magnetic Declination

The Earth is not just a simple magnet. The compass points to an average of the fields.

Adjusting your compass to allow for local magnetic declination will ensure you know the true direction of True or Geographic North.

The earth rotates around the True North to True South axis and the Celestrial Poles are above that axis. An Equatorial Mount needs to be physically aligned with this axis to prevent field rotation within long exposure images.

A video on the moving magnetic pole.
A YouTube video (by Anton Petrov in May 2020) with some good graphics showing the complexity of the magnetic fields and why it's important to know the local magnetic declination. You might notice at time point 2:28 in the video, the magnet drawn in the middle of the earth has its south pole aligned with true north meaning the north magnetic pole is magnetically south (so our magnetised compass needles north end will point to the magnetically south but geographically north pole).

Some online calculators for finding your Magnetic Declination:

• Australian Government Geomagnetic Reference Field Values
• NDGC Find the magnetic declination
• USA NOAA Magnetic Declination Estimated Value

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