Polaris coordinates shift with time because of precession

Stellarium (a free, downloadable software program) has a nice little feature showing you the coordinates for all the stars (that you click on in the program to see the features for each star). Looking at the graphic above, you can see Polaris has celestial coordinates as shown for today (J2019.5), and another set of coordinates showing Polaris’ position back on January 1, 2000 (J2000). Why is that? 

Polaris’ coordinates, and all the rest of the stars’ coordinates in the sky, change continuously . This is because the Earth’s axis precesses continuously. Precession, or the wobbling of the Earth’s axis, can only occur when the Earth rotates ! (https://en.wikipedia.org/wiki/Precession) 

One complete “wobble,” of the Earth’s axis (like a spinning top), takes 26,000 years. So in 19 and a half years, the declination (north/south position) of Polaris has only shifted ~5 minutes of arc. In comparison, the Moon is roughly 30 minutes of arc in diameter. Thus, the Earth’s rotation can be seen if you look at the coordinates for each star over time! The change in coordinates is small in a 20 year period but measurable!

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