The Chandler Wobble
Earth precesses around its axis every ~26000 years.
But in addition to this precession, there is an extra wobble that was observed by Kustner and later followed up by Seth Carlo Chandler, Jr called the Chandler Wobble that occurs at a much smaller time scale.
In 1888, Kustner found that the latitude of Berlin had changed slightly
during his observations of the night sky.
Therefore in 1891,Chandler. decided to conduct a 14 month study examining this change. The following is a plot of the spiral path taken by the earth’s axis over that 14 month period.
The following plot shows the motion from 1909 – 2001.
Although many theories indicate that this is due to the fact that earth is not a perfect spherical rigid body, it is still not entirely clear on the mechanism that drives earth into this small wobbly motion.
If you took a closer look at the plots you would find that this wobble is of the order of a couple of meters which most certainly does not seem like a lot.
But if you are an astronomer if you do not account for this correction, you might just end up pointing your telescope at the wrong object
Have a great day!