<p>Here's an animation I found that gives you an idea of the movements and timescales involved:</p>
<p><div class="youtube-embed"><div>
                <iframe width="640px" height="395px" src="https://www.youtube.com/embed/sNqVRzjTSFg?start=0"></iframe>
            </div></div></p>
<p>It depicts the estimated movement of the Orion Constellation from 3 million years in the past to 3 million years in the future.</p>

CC BY-SA 4.0
2021-06-14T15:07:28.647Z
Poor Betelgeuse...
frarugi87
CC BY-SA 4.0
2021-06-14T02:10:28.387Z
2021-06-14T02:10:28.387Z
Ingolifs
<p>The Milky Way takes 225-250 Million years for one rotation (at Sol's radius).</p>
<p>Humanity has been here, and looking up, for, at most (and to make the numbers easier) 10,000 years.</p>
<p>10,000 / 250,000,000 = 0.00004</p>
<p>We (humanity) have been seeing stars for 4 hundred-thousandths of a revolution, or 0.0144 degrees of rotation.</p>
<p>The constellations change, we just haven't been watching long enough. Check again in a few million years.</p>

CC BY-SA 4.0
2021-06-15T16:26:40.147Z
2021-06-15T23:31:14.120Z
2021-06-15T23:31:14.120Z
waltinator
<p>Yes, the shape of the constellation does and will change over time. All the stars have their own peculiar velocities and have some random motion which over time will ruin all the constellations. However, Even though the stars are moving at rapid speeds, to us, in our sky, due to their enormous distance from us, they appear to move extremely slowly and the constellations can stay the way they are for another few hundred/thousand years until we notice any visible change (Naked eyes observations).</p>
<p><em>Those slow relative changes in position give each star in our sky a particular &quot;proper motion&quot;—a change in angular position. The proper motion of most stars is extremely small, measured in milli-arcseconds per year, where an arcsecond is 1/3600 of a degree, and of course milli means a thousandth of that. Hold up your pinky finger at arm's length: the width of your pinky, expressed as an angle, is about one degree, give or take. One degree is 3,600 arcseconds, or 3,600,000 milli-arcseconds.</em></p>
<p><em><a href="https://en.wikipedia.org/wiki/Proper_motion" rel="nofollow noreferrer">Proper motion</a>, in astronomy, the apparent motion of a star across the celestial sphere at right angles to the observer’s line of sight; any radial motion (toward or away from the Sun) is not included.</em></p>
<p>The fastest star in our current sky is Barnard's Star, which is moving radially at 110km/s towards us, has a proper motion of only 10.3 arc-seconds (which is the fastest proper motion in our sky). This means, in another 350 years, it would only move around 1 pinky finger-width.</p>
<p>Here is the <a href="https://www.kqed.org/quest/41313/do-constellations-change-over-time" rel="nofollow noreferrer">source</a> if you want to read more.</p>

CC BY-SA 4.0
2021-06-12T21:07:44.777Z
Despite its closeness, Barnard's Star is not visible to the naked eye. Only a few stars that we can see with our naked eyes have a significant proper motion. I am not disagreeing with your answer. (Plus one, BTW.)
David Hammen
CC BY-SA 4.0
2021-06-13T04:10:58.550Z
Also, although the stars are moving rapidly, we are also moving.  Most of the motion of the stars close to us - which are most of the ones we see - is in roughly the same direction as the sun is moving.  It's rather like being in (non-rush hour) freeway traffic: all the cars may be moving at say roughly 70 mph, but you only notice their relative motions.
jamesqf
CC BY-SA 4.0
2021-06-13T23:30:06.680Z
"*has a proper motion of only 10.3 arc-seconds*". That's 10.3 arc-second/year, isn't it?
Abigail
CC BY-SA 4.0
2021-06-14T02:40:13.213Z
@Abigail  "The proper motion of most stars is extremely small, measured in milli-arcseconds per year." Yes, it is 10.3 arc-seconds per year.
Aryan Bansal
CC BY-SA 4.0
2021-06-14T07:32:06.763Z
Related: Looking down on a seemingly static ocean (with discernible ships and waves) from an airplane, or looking down on a seemingly stationary LA from Mt. Wilson (it took me a minute to understand that the non-moving strings of lights were *actually moving cars.)*
Peter - Reinstate Monica
CC BY-SA 4.0
2021-06-14T22:22:31.480Z
_"moving radially ... away from us"_ — this sounds like a poor example of a rapidly moving star: its tangential speed in Earth-centric frame is much smaller than 110 km/s.
Ruslan
CC BY-SA 4.0
2021-06-15T09:02:55.470Z
@Ruslan Yes, maybe it sounds confusing. _Proper motion, in astronomy, the apparent motion of a star across the celestial sphere at right angles to the observer’s line of sight; any radial motion (toward or away from the Sun) is not included._ Barnard's star has the fastest proper motion (hence fastest transverse velocity)
Aryan Bansal
CC BY-SA 4.0
2021-06-15T09:26:49.080Z
@Ruslan I have edited the answer a little hoping that it's much clearer now.
Aryan Bansal
CC BY-SA 4.0
2021-06-12T19:41:13.203Z
2021-06-16T13:44:08.913Z
2021-06-16T13:44:08.913Z
Aryan Bansal
<p>From what I understood, the Milky Way (or stars in the Milky Way) doesn't rotate like a collection of points in a disc due to the presence of some invisible matter. In theory, the angular velocities of all the stars should be the same while linear velocities should decrease as the radial distance increases. But in reality, linear velocities stay almost the same as we move farther from the galactic center. But that will decrease the angular velocity yes, right?</p>
<p>And I know that stars in a constellation are usually far apart. So this implies they have different angular velocities around the galactic center/nucleus. Then how does the shape of constellations stays the same? If stars are rotating at different angular velocities, will the constellations get distorted over time?</p>

CC BY-SA 4.0
2021-06-12T19:18:57.027Z
Related: https://astronomy.stackexchange.com/a/39527/16685
PM 2Ring
CC BY-SA 4.0
2021-06-12T20:40:32.483Z
Check out this to see what happens to Orion https://youtu.be/MK6v9G06Ks8
ProfRob
CC BY-SA 4.0
2021-06-13T10:06:53.300Z
_How are constellations intact_ Not.
TaW
CC BY-SA 4.0
2021-06-13T17:07:08.683Z
"In theory, the angular velocities of all the stars should be the same" This is not true even excluding dark matter.  Earth takes a year to go around the sun, Mercury takes ~3 months, Pluto takes ~250 years.  Clearly objects in orbit can have different angular velocities.
Ryan_L
CC BY-SA 4.0
2021-06-13T17:14:09.487Z
The star Arcturus was located in a different place during Hipparchus and Ptolemy’s times. William Herschel noticed that and was the first to propose the concept of stellar proper motion.
Pierre Paquette
CC BY-SA 4.0
2021-06-13T20:32:20.213Z
Linear velocities do not at all remain constant as distance from the center increases, "in theory" or otherwise. Isaac Newton worked that out.
Michael Hardy
CC BY-SA 4.0
2021-06-13T20:43:41.607Z
Another fine movie of stellar motion: https://www.youtube.com/watch?v=Ag0qsSFJBAk&t=33s
John Doty
CC BY-SA 4.0
2021-06-14T12:17:36.507Z
@MichaelHardy linear velocities do remain constant with distance from the centre of the galaxy. That is an experimental fact that leads to idea of dark matter.
ProfRob
CC BY-SA 4.0
2021-06-14T19:28:06.043Z
The free program [Digital Universe](https://www.amnh.org/research/hayden-planetarium/digital-universe) shows the movement over time. (Read the [manual](https://www.haydenplanetarium.org/downloads/universe/Partiview-Quick-Start-Guide.pdf) before attempting to use - it's not an intuitive user interface)
Aaron F
CC BY-SA 4.0
2021-06-15T17:23:02.197Z
See also: https://astronomy.stackexchange.com/questions/16597/do-constellations-change
Amazon Dies In Darkness
<star><galaxy><rotation><constellations>
How are constellations intact if the stars are rotating around galactic nuclei?
Muhammed Roshan
# How are constellations intact if the stars are rotating around galactic nuclei?

(Asked by: username_0 on 2021-06-12)

From what I understood, the Milky Way (or stars in the Milky Way) doesn't rotate like a collection of points in a disc due to the presence of some invisible matter. In theory, the angular velocities of all the stars should be the same while linear velocities should decrease as the radial distance increases. But in reality, linear velocities stay almost the same as we move farther from the galactic center. But that will decrease the angular velocity yes, right?

And I know that stars in a constellation are usually far apart. So this implies they have different angular velocities around the galactic center/nucleus. Then how does the shape of constellations stays the same? If stars are rotating at different angular velocities, will the constellations get distorted over time?

**Tags:** star, galaxy, rotation, constellations
> **Comments:**
> **username_1**: Related: https://astronomy.stackexchange.com/a/39527/16685  
> **username_2**: Check out this to see what happens to Orion https://youtu.be/MK6v9G06Ks8  
> **username_3**: _How are constellations intact_ Not.  
> **username_4**: "In theory, the angular velocities of all the stars should be the same" This is not true even excluding dark matter.  Earth takes a year to go around the sun, Mercury takes ~3 months, Pluto takes ~250 years.  Clearly objects in orbit can have different angular velocities.  
> **username_5**: The star Arcturus was located in a different place during Hipparchus and Ptolemy’s times. William Herschel noticed that and was the first to propose the concept of stellar proper motion.  
> **username_6**: Linear velocities do not at all remain constant as distance from the center increases, "in theory" or otherwise. Isaac Newton worked that out.  
> **username_7**: Another fine movie of stellar motion: https://www.youtube.com/watch?v=Ag0qsSFJBAk&t=33s  
> **username_2**: @MichaelHardy linear velocities do remain constant with distance from the centre of the galaxy. That is an experimental fact that leads to idea of dark matter.  
> **username_8**: The free program [Digital Universe](https://www.amnh.org/research/hayden-planetarium/digital-universe) shows the movement over time. (Read the [manual](https://www.haydenplanetarium.org/downloads/universe/Partiview-Quick-Start-Guide.pdf) before attempting to use - it's not an intuitive user interface)  
> **username_9**: See also: https://astronomy.stackexchange.com/questions/16597/do-constellations-change  

---

## 3 answers

### Answer by username_13 on 2021-06-12. Score: 51 | Accepted answer

Yes, the shape of the constellation does and will change over time. All the stars have their own peculiar velocities and have some random motion which over time will ruin all the constellations. However, Even though the stars are moving at rapid speeds, to us, in our sky, due to their enormous distance from us, they appear to move extremely slowly and the constellations can stay the way they are for another few hundred/thousand years until we notice any visible change (Naked eyes observations).

*Those slow relative changes in position give each star in our sky a particular "proper motion"—a change in angular position. The proper motion of most stars is extremely small, measured in milli-arcseconds per year, where an arcsecond is 1/3600 of a degree, and of course milli means a thousandth of that. Hold up your pinky finger at arm's length: the width of your pinky, expressed as an angle, is about one degree, give or take. One degree is 3,600 arcseconds, or 3,600,000 milli-arcseconds.*

*[Proper motion](https://en.wikipedia.org/wiki/Proper_motion), in astronomy, the apparent motion of a star across the celestial sphere at right angles to the observer’s line of sight; any radial motion (toward or away from the Sun) is not included.*

The fastest star in our current sky is Barnard's Star, which is moving radially at 110km/s towards us, has a proper motion of only 10.3 arc-seconds (which is the fastest proper motion in our sky). This means, in another 350 years, it would only move around 1 pinky finger-width.

Here is the [source](https://www.kqed.org/quest/41313/do-constellations-change-over-time) if you want to read more.

> **Comments:**
> **username_14**: Despite its closeness, Barnard's Star is not visible to the naked eye. Only a few stars that we can see with our naked eyes have a significant proper motion. I am not disagreeing with your answer. (Plus one, BTW.)  
> **username_15**: Also, although the stars are moving rapidly, we are also moving.  Most of the motion of the stars close to us - which are most of the ones we see - is in roughly the same direction as the sun is moving.  It's rather like being in (non-rush hour) freeway traffic: all the cars may be moving at say roughly 70 mph, but you only notice their relative motions.  
> **username_16**: "*has a proper motion of only 10.3 arc-seconds*". That's 10.3 arc-second/year, isn't it?  
> **username_13**: @Abigail  "The proper motion of most stars is extremely small, measured in milli-arcseconds per year." Yes, it is 10.3 arc-seconds per year.  
> **username_17**: Related: Looking down on a seemingly static ocean (with discernible ships and waves) from an airplane, or looking down on a seemingly stationary LA from Mt. Wilson (it took me a minute to understand that the non-moving strings of lights were *actually moving cars.)*  
> **username_18**: _"moving radially ... away from us"_ — this sounds like a poor example of a rapidly moving star: its tangential speed in Earth-centric frame is much smaller than 110 km/s.  
> **username_13**: @Ruslan Yes, maybe it sounds confusing. _Proper motion, in astronomy, the apparent motion of a star across the celestial sphere at right angles to the observer’s line of sight; any radial motion (toward or away from the Sun) is not included._ Barnard's star has the fastest proper motion (hence fastest transverse velocity)  
> **username_13**: @Ruslan I have edited the answer a little hoping that it's much clearer now.  

---

### Answer by username_10 on 2021-06-14. Score: 21

Here's an animation I found that gives you an idea of the movements and timescales involved:

It depicts the estimated movement of the Orion Constellation from 3 million years in the past to 3 million years in the future.

> **Comments:**
> **username_11**: Poor Betelgeuse...  

---

### Answer by username_12 on 2021-06-15. Score: 4

The Milky Way takes 225-250 Million years for one rotation (at Sol's radius).

Humanity has been here, and looking up, for, at most (and to make the numbers easier) 10,000 years.

10,000 / 250,000,000 = 0.00004

We (humanity) have been seeing stars for 4 hundred-thousandths of a revolution, or 0.0144 degrees of rotation.

The constellations change, we just haven't been watching long enough. Check again in a few million years.


---

