This figure shows what you would see if you stood near the north geographic pole and measured the rotation axis position. This can be done by carefully following the motion of the stars near your zenith (straight over head). In practice, it is done by using radio interferometers elsewhere on the planet and 'solving' for changes in the positions of cosmic radio sources located at many different spots on the sky.
I have additional answers to this 'question' elsewhere at the Ask the Astronomer site, so have a look at these other answers too for more details. The US Naval Observatory in Washington DC is a part of this world-wide network studying the high-precision rotation of the Earth which has a big impact on the length of day and time keeping practices.
Copyright 1997 Dr. Sten Odenwald
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