<p>Barry Carter's <strong>nice piece of work</strong> contains 50 stars within <span class="math-container">$\sim 74$</span> light years of Betelegeuse.</p>

<p>Leaving aside the question marks over exactly where Betelegeuse is (in terms of distance) and the parallax uncertainties of the 50 stars listed, there is also the problem that the faintest stars in the HYG catalogue are based on the Hipparcos catalogue, which is only complete to something like 8th magnitude, though it does contain some stars down to about 10th mag. If we assume that Betelgeuse is at around 700 light years (214 pc), then a magnitude of 10, corresponds to an absolute magnitude of about 3.3. These stars are very luminous indeed, about 3 times as luminous as the Sun or more, so either upper main sequence stars are giants.</p>

<p>Upper main sequence stars and giants form a tiny fraction of the local stellar population (and one presumes the locale around Betelgeuse since it is only 30 pc below the Galactic plane) - see for example this plot from  <a href="https://iopscience.iop.org/article/10.1088/0143-0807/24/2/303" rel="noreferrer">Jeffries &amp; Elliott (2003)</a>, which shows an absolute magnitude vs colour (HR) diagram for 1000 stars within <span class="math-container">$\sim 15$</span> pc of the Sun. As you can see, objects with <span class="math-container">$M_V&lt;3.3$</span> are rare, perhaps <span class="math-container">$\sim 2$</span>% of the population.</p>

<p><a href="https://i.sstatic.net/UXYzM.png" rel="noreferrer"><img src="https://i.sstatic.net/UXYzM.png" alt="Local HRD"></a></p>

<p>So the point of this is, that assuming Betelegeuse isn't sitting in a void, or in a cluster (which as far as we know, it isn't) then the stellar density around it is at least (and I say at least, because there is no way that the catalogue I used to produce the picture above is complete beyond spectral type M3-M4) is at least 0.07 stars per cubic parsec, or 0.002 stars per cubic light year.</p>

<p>If that is the case, then there should be at least 3400 stars within 74 light years of Betelgeuse and <strong>finally</strong> (the whole point of this "answer"), the nearest star to Betelgeuse is likely to be separated from it by <span class="math-container">$1/(0.002)^{1/3} =  7.9$</span> light years.</p>

<p>Unfortunately, it is an "answer" because we are no closer to knowing <strong>which</strong> star that is! Gaia DR2 (and DR3 later in 2020) would help in completing the census, since it has (or will have) parallaxes for stars down to about <span class="math-container">$V\sim 19$</span> (absolute magnitude of about 12.3 at the distance of Betelgeuse) and should then include about 60-70% of stars in its vicinity. However, Gaia will not (I think) yield an accurate parallax for Betelgeuse because it is too bright(!), so we will be no further forward in answering the question.</p>

CC BY-SA 4.0
2020-03-05T20:13:15.930Z
And for all we know there's some star sitting a few light years directly behind Betelgeuse so we can't (currently) see it.
PM 2Ring
CC BY-SA 4.0
2020-03-05T18:49:03.380Z
2020-03-05T18:49:03.380Z
ProfRob
<p>Based on <a href="https://physics.stackexchange.com/a/455544/72564">this answer</a>, I should be able to figure out <a href="https://astronomy.stackexchange.com/q/35137/9527">this question</a>, if I know the distance between Betelgeuse and its nearest neighbor. So what is Betelgeuse's nearest neighbor? </p>

<p>I do mean the nearest neighbor in 3D space, not in the plane of the sky. Since Betelgeuse is fairly close to the Sun, I'm guessing we should know its neighborhood with a pretty good precision. </p>

CC BY-SA 4.0
2020-02-27T08:58:12.030Z
The star closest was of course Michael Keaton
uhoh
CC BY-SA 4.0
2020-02-27T12:14:08.183Z
Note that the margin of error for star distances (including Betelgeuse) is quite large.  [Wikipedia's page discusses several estimates](https://en.wikipedia.org/wiki/Betelgeuse#Distance_measurements), but a recent value is 720 lyr with an error range of about $\pm$120 lyr.  So distances to the nearest star to Betelgeuse are probably meaningless calculations as the margins of error will be huge.
StephenG - Help Ukraine
CC BY-SA 4.0
2020-02-27T16:50:33.420Z
@barry Unfortunately, according to the Wikipedia article linked by StephenG, "So far for Gaia DR2 there is no data on Betelgeuse".
PM 2Ring
CC BY-SA 4.0
2020-02-27T18:30:40.383Z
Betelgeuse is too bright for Gaia. However if you can get coordinates for Betelguese is should be possible to search the area around it for stars in the Gaia catalogue.
Steve Linton
<star><distances><betelgeuse>
What star is the closest to Betelgeuse?
usernumber
# What star is the closest to Betelgeuse?

(Asked by: username_0 on 2020-02-27)

Based on [this answer](https://physics.stackexchange.com/a/455544/72564), I should be able to figure out [this question](https://astronomy.stackexchange.com/q/35137/9527), if I know the distance between Betelgeuse and its nearest neighbor. So what is Betelgeuse's nearest neighbor?

I do mean the nearest neighbor in 3D space, not in the plane of the sky. Since Betelgeuse is fairly close to the Sun, I'm guessing we should know its neighborhood with a pretty good precision.

**Tags:** star, distances, betelgeuse
> **Comments:**
> **username_1**: The star closest was of course Michael Keaton  
> **username_2**: Note that the margin of error for star distances (including Betelgeuse) is quite large.  [Wikipedia's page discusses several estimates](https://en.wikipedia.org/wiki/Betelgeuse#Distance_measurements), but a recent value is 720 lyr with an error range of about $\pm$120 lyr.  So distances to the nearest star to Betelgeuse are probably meaningless calculations as the margins of error will be huge.  
> **username_3**: @barry Unfortunately, according to the Wikipedia article linked by StephenG, "So far for Gaia DR2 there is no data on Betelgeuse".  
> **username_4**: Betelgeuse is too bright for Gaia. However if you can get coordinates for Betelguese is should be possible to search the area around it for stars in the Gaia catalogue.  

---

## 1 answers

### Answer by username_5 on 2020-03-05. Score: 7

Barry Carter's **nice piece of work** contains 50 stars within $\sim 74$ light years of Betelegeuse.

Leaving aside the question marks over exactly where Betelegeuse is (in terms of distance) and the parallax uncertainties of the 50 stars listed, there is also the problem that the faintest stars in the HYG catalogue are based on the Hipparcos catalogue, which is only complete to something like 8th magnitude, though it does contain some stars down to about 10th mag. If we assume that Betelgeuse is at around 700 light years (214 pc), then a magnitude of 10, corresponds to an absolute magnitude of about 3.3. These stars are very luminous indeed, about 3 times as luminous as the Sun or more, so either upper main sequence stars are giants.

Upper main sequence stars and giants form a tiny fraction of the local stellar population (and one presumes the locale around Betelgeuse since it is only 30 pc below the Galactic plane) - see for example this plot from [Jeffries & Elliott (2003)](https://iopscience.iop.org/article/10.1088/0143-0807/24/2/303), which shows an absolute magnitude vs colour (HR) diagram for 1000 stars within $\sim 15$ pc of the Sun. As you can see, objects with $M\_V<3.3$ are rare, perhaps $\sim 2$% of the population.

[![Local HRD](https://i.sstatic.net/UXYzM.png)](https://i.sstatic.net/UXYzM.png)

So the point of this is, that assuming Betelegeuse isn't sitting in a void, or in a cluster (which as far as we know, it isn't) then the stellar density around it is at least (and I say at least, because there is no way that the catalogue I used to produce the picture above is complete beyond spectral type M3-M4) is at least 0.07 stars per cubic parsec, or 0.002 stars per cubic light year.

If that is the case, then there should be at least 3400 stars within 74 light years of Betelgeuse and **finally** (the whole point of this "answer"), the nearest star to Betelgeuse is likely to be separated from it by $1/(0.002)^{1/3} = 7.9$ light years.

Unfortunately, it is an "answer" because we are no closer to knowing **which** star that is! Gaia DR2 (and DR3 later in 2020) would help in completing the census, since it has (or will have) parallaxes for stars down to about $V\sim 19$ (absolute magnitude of about 12.3 at the distance of Betelgeuse) and should then include about 60-70% of stars in its vicinity. However, Gaia will not (I think) yield an accurate parallax for Betelgeuse because it is too bright(!), so we will be no further forward in answering the question.

> **Comments:**
> **username_3**: And for all we know there's some star sitting a few light years directly behind Betelgeuse so we can't (currently) see it.  

---

