<p>The right ascension and declination of stars change on a day to day basis. Some of the changes are quite large. The right ascension of Polaris, for example, changes by more than a degree over the course of some years. The excursions are irregular. Their time and extent differ from year to year. I know that precession will change coordinates of all the stars over tens of thousands of years, but I can't find an explanation for these short term changes. </p>

<p>Polaris started 2017 with a sidereal hour angle of 316 deg 23.9 min. The SHA increased monotonically to 317  3.6 by the end of April, then decreased in small steps to 315  58.3 by November 9, then increased again, ending the year at 316 
 6.2.</p>

CC BY-SA 4.0
2019-06-01T15:41:00.060Z
Could you quantify "quite large"? Every star has its proper motion, e.e. we see them as they move through 3D space relative to us, this causes coordinates to change with time. Proper motion values of stars are known. So if you would quantify what you've seen, one could compare those values.
AtmosphericPrisonEscape
CC BY-SA 4.0
2019-06-01T18:50:56.017Z
I found the answer. Explained very well in the Wikipedia article on Nutation. I was led to "nutation" by following links I found searching on "proper motion." The question should be closed. Thanks, @atmosphericprisonescape
stretch
CC BY-SA 4.0
2019-06-01T23:19:14.067Z
@stretch It is always okay to answer your own question in Stack Exchange. If you feel you've figured out what you want to know, feel free to post an answer!
uhoh
CC BY-SA 4.0
2019-06-01T23:30:52.580Z
To reinforce @uhoh's comment, I would be genuinely interested in reading (and upvoting) an answer - and by providing it yourself, you would be in the running for a relatively rare badge: [Self-learner](https://astronomy.stackexchange.com/help/badges/14/self-learner)!
Chappo Hasn't Forgotten
<observational-astronomy>
Short term changes in celestial coordinates of stars
stretch
# Short term changes in celestial coordinates of stars

(Asked by: username_0 on 2019-06-01)

The right ascension and declination of stars change on a day to day basis. Some of the changes are quite large. The right ascension of Polaris, for example, changes by more than a degree over the course of some years. The excursions are irregular. Their time and extent differ from year to year. I know that precession will change coordinates of all the stars over tens of thousands of years, but I can't find an explanation for these short term changes.

Polaris started 2017 with a sidereal hour angle of 316 deg 23.9 min. The SHA increased monotonically to 317 3.6 by the end of April, then decreased in small steps to 315 58.3 by November 9, then increased again, ending the year at 316
6.2.

**Tags:** observational-astronomy
> **Comments:**
> **username_1**: Could you quantify "quite large"? Every star has its proper motion, e.e. we see them as they move through 3D space relative to us, this causes coordinates to change with time. Proper motion values of stars are known. So if you would quantify what you've seen, one could compare those values.  
> **username_0**: I found the answer. Explained very well in the Wikipedia article on Nutation. I was led to "nutation" by following links I found searching on "proper motion." The question should be closed. Thanks, @atmosphericprisonescape  
> **username_2**: @stretch It is always okay to answer your own question in Stack Exchange. If you feel you've figured out what you want to know, feel free to post an answer!  
> **username_3**: To reinforce @uhoh's comment, I would be genuinely interested in reading (and upvoting) an answer - and by providing it yourself, you would be in the running for a relatively rare badge: [Self-learner](https://astronomy.stackexchange.com/help/badges/14/self-learner)!  

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## 0 answers

