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If one observes the Earth from an independent (inertial) reference frame, one would observe the following movements.

1. Earth rotates on its axis about once per day.
2. Every lunar month, the Earth-Moon

system rotates about its barycenter, the center of mass point on a line drawn between the center of Earth and the center of the moon. The point is approximately 1,710 km (1062 miles) below the surface of the Earth.
3. Earth wobbles, which is a way of saying there is "polar motion" and the north-south

axis of rotation changes in a sort of regular fashion. There are little wobbles (The Chandler Wobble) every 433 days and other wobbles over years and one grand wobble over 26,000 years. Wobbling is due to the mass distribution around Earth and is influenced by melting glaciers and earthquakes. This means the north geographic pole changes by a few meters a year. (This is not to be confused with changes in the magnetic poles which is measured in kilometers per year.)
4. Earth is in orbit around the Sun, a movement which takes a whole year.
5. The orbit of Earth around the Sun has a small wobbly character. The Earth's rotation about the Sun is not the same every year and is influenced by a number of factors, including the gravitational pull of other planets. The consequences, referred to as Milankovitch

cycles, are changes in the orbital eccentricity, obliquity, and precession of the Earth's orbit over time frames of perhaps a 100,000 years.
6. The Sun rotates around with the other stars as we swirl in the Milky Way galaxy which takes over a billion years to complete.
7. As the Solar system rotate around the Milky Way, it also undergoes an up and down motion rising above and then moving below the galactic plane. The full cycle takes 70-80 billion years.



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12y ago

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