Page "North Pole" Paragraph 6

The Earth's axis of rotation – and hence the position of the North Pole – was commonly believed to be fixed ( relative to the surface of the Earth ) until, in the 18th century, the mathematician Leonhard Euler predicted that the axis might " wobble " slightly.

Around the beginning of the 20th century astronomers noticed a small apparent " variation of latitude ," as determined for a fixed point on Earth from the observation of stars.

Part of this variation could be attributed to a wandering of the Pole across the Earth's surface, by a range of a few meters.

The wandering has several periodic components and an irregular component.

The component with a period of about 435 days is identified with the 8 month wandering predicted by Euler and is now called the Chandler wobble after its discoverer.

The exact point of intersection of the Earth's axis and the Earth's surface, at any given moment, is called the " instantaneous pole ", but because of the " wobble " this cannot be used as a definition of a fixed North Pole ( or South Pole ) when metre-scale precision is required.