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Find the point directly opposite you on the other side of the Earth. For a location on the black outline map, that spot on the inverted red map (or vice-versa) will be your Local Nadir, or Antipode.
[The King of the Formorians]
"wondered why the sun rose one morning in the west, instead of the customary east"
cited in, The Celts, Frank Delany, BBC Publications, Hodder and Stoughton, London, 1986 p. 61
By magnetic reversal, or 'flip', we mean the process by which the North pole is transformed into a South pole and the South pole becomes a North pole.
We have no complete record of the history of any reversal.
We have limited evidence from geological measurements about the patterns of change in the magnetic field during a reversal.
Magnetic Reversals
Considering that ships, planes and Boy Scouts steer by it, Earth's magnetic field is less reliable than you'd think. Rocks in an ancient lava flow in Oregon suggest that for a brief erratic span about 16 million years ago magnetic north shifted as much as 6 degrees per day. After little more than a week, a compass needle would have pointed toward Mexico City.When North goes South
Even so, the current strength of the magnetic field is as high as it has been in the last 50,000 years, even if it is nearly 800,000 years since the last reversal.
Originally posted by Phage
Can you tell my how antipodes are important in astronomy?
There is plenty of information on magnetic reversals. The last one occurred quite a long time ago, as your source says:
Even so, the current strength of the magnetic field is as high as it has been in the last 50,000 years, even if it is nearly 800,000 years since the last reversal.