<p>These stars are currently moving away from us, in the case of Epsilon Eridani, at 15.5 km/s. In 31500 years they will be further away than they are now, the distance can be calculated by applying Pythagoras' theorem to the distances and velocities you mention.</p>

<p>It turns out that Eps Eri will be about 12.2 light years from Earth, and Lutyen 726-8 will be 12.6 light years.</p>

<p>They won't be particularly close together in the sky, I estimate about 3 degrees, and they will be even dimmer than they are now, though Eps Eri will still be a naked eye object.</p>

CC BY-SA 3.0
2016-05-24T05:24:12.380Z
Woah great answer, with interesting details! I still have to look about how you applied Pythagora's theorem and what variable you used, but you perfectly answered my question, thank you!
Tepec
CC BY-SA 3.0
2016-05-23T21:30:36.353Z
2016-05-23T21:30:36.353Z
James K
<p>Based on <a href="https://en.wikipedia.org/wiki/Epsilon_Eridani#Kinematics" rel="nofollow noreferrer">Wikipedia</a> and more precisely <a href="https://arxiv.org/pdf/1004.1557v1.pdf" rel="nofollow noreferrer">this paper</a>, it is said that, in about 31,500 years, the stars <a href="http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-ref=VIZ574369b052ac&amp;-out.add=.&amp;-source=V/137D/XHIP&amp;recno=16495" rel="nofollow noreferrer">Epsilon Eridani</a> and Luyten <a href="http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-ref=VIZ57436a7d67ce&amp;-out.add=.&amp;-source=V/137D/XHIP&amp;recno=36100" rel="nofollow noreferrer">726-8AB</a> will &quot;meet&quot; at a very close distance (less than 1 light year). I found that anecdote very interesting in the context of some SF writings I'm trying to do (not in English) to bring some &quot;subtle consistency&quot; in it, but I was unable to either answer nor calculate what distance will those stars be from the Solar System in 31,500 years?</p>
<p>Here is some potentially useful information:</p>
<ul>
<li><p><strong>Current distance from Epsilon Eridani to Solar System:</strong> 10.5ly</p>
</li>
<li><p><strong>Current distance from Luyten 726-8 to Solar System:</strong> 8.7ly</p>
</li>
<li><p><strong>Other info about Epsilon Eridani:</strong> declination 9.46° south of the celestial equator | Right Ascension 03h 32m 55.84496s | Radial velocity +15.5 ± 0.9 km/s</p>
</li>
<li><p><strong>Other info about Luyten 726-8:</strong> declination –17° 57′ 01.8″ | Right Ascension      01h 39m 01.54s | Radial velocity +29.0 km/s</p>
</li>
</ul>

CC BY-SA 3.0
2016-05-23T20:04:25.480Z
The information that is not present here is anything about their velocity vectors, and that seems like what you would need to answer this question.
SE - stop firing the good guys
CC BY-SA 3.0
2016-05-23T20:12:16.973Z
As well as the declination of the star you also need there RA and as Hohmannfan says their velocity vectors.
James Screech
CC BY-SA 3.0
2016-05-23T20:14:10.087Z
@Hohmannfan Hi! I have absolutely no idea as of where I could find this info and how I could use them ..! But from that paper I quoted, there's this: "Let us denote Epsilon Eridani by X and BL/UV Ceti by Y (...). [D]istance dXY = k~rXY k between Epsilon Eridani and Luyten 726-8 is
≈ 5.09 ly. Radial velocities of stars X and Y are vr,X = 16.3±0.1 (PCRV) and vr,Y = 21.9 ± 0.1 (Malaroda et al.). We will also use an older
measurement vr,Y = 29 ± 2 from GCRV".
Tepec
CC BY-SA 3.0
2016-05-23T20:16:25.117Z
@JamesScreech Thanks also for your answer! I'm assuming that "RA" is "Right Ascension"; I'll find those info and edit my post to add them in it.
Tepec
<star><movement><kinematics><future>
In 31.5kyr, Epsilon Eridani and Luyten 726-8 will be < 1ly close; but how distant from the Solar system?
Tepec
# In 31.5kyr, Epsilon Eridani and Luyten 726-8 will be < 1ly close; but how distant from the Solar system?

(Asked by: username_0 on 2016-05-23)

Based on [Wikipedia](https://en.wikipedia.org/wiki/Epsilon_Eridani#Kinematics) and more precisely [this paper](https://arxiv.org/pdf/1004.1557v1.pdf), it is said that, in about 31,500 years, the stars [Epsilon Eridani](http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-ref=VIZ574369b052ac&-out.add=.&-source=V/137D/XHIP&recno=16495) and Luyten [726-8AB](http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-ref=VIZ57436a7d67ce&-out.add=.&-source=V/137D/XHIP&recno=36100) will "meet" at a very close distance (less than 1 light year). I found that anecdote very interesting in the context of some SF writings I'm trying to do (not in English) to bring some "subtle consistency" in it, but I was unable to either answer nor calculate what distance will those stars be from the Solar System in 31,500 years?

Here is some potentially useful information:

* **Current distance from Epsilon Eridani to Solar System:** 10.5ly
* **Current distance from Luyten 726-8 to Solar System:** 8.7ly
* **Other info about Epsilon Eridani:** declination 9.46° south of the celestial equator | Right Ascension 03h 32m 55.84496s | Radial velocity +15.5 ± 0.9 km/s
* **Other info about Luyten 726-8:** declination –17° 57′ 01.8″ | Right Ascension 01h 39m 01.54s | Radial velocity +29.0 km/s

**Tags:** star, movement, kinematics, future
> **Comments:**
> **username_1**: The information that is not present here is anything about their velocity vectors, and that seems like what you would need to answer this question.  
> **username_2**: As well as the declination of the star you also need there RA and as Hohmannfan says their velocity vectors.  
> **username_0**: @Hohmannfan Hi! I have absolutely no idea as of where I could find this info and how I could use them ..! But from that paper I quoted, there's this: "Let us denote Epsilon Eridani by X and BL/UV Ceti by Y (...). [D]istance dXY = k~rXY k between Epsilon Eridani and Luyten 726-8 is ≈ 5.09 ly. Radial velocities of stars X and Y are vr,X = 16.3±0.1 (PCRV) and vr,Y = 21.9 ± 0.1 (Malaroda et al.). We will also use an older measurement vr,Y = 29 ± 2 from GCRV".  
> **username_0**: @JamesScreech Thanks also for your answer! I'm assuming that "RA" is "Right Ascension"; I'll find those info and edit my post to add them in it.  

---

## 1 answers

### Answer by username_3 on 2016-05-23. Score: 5 | Accepted answer

These stars are currently moving away from us, in the case of Epsilon Eridani, at 15.5 km/s. In 31500 years they will be further away than they are now, the distance can be calculated by applying Pythagoras' theorem to the distances and velocities you mention.

It turns out that Eps Eri will be about 12.2 light years from Earth, and Lutyen 726-8 will be 12.6 light years.

They won't be particularly close together in the sky, I estimate about 3 degrees, and they will be even dimmer than they are now, though Eps Eri will still be a naked eye object.

> **Comments:**
> **username_0**: Woah great answer, with interesting details! I still have to look about how you applied Pythagora's theorem and what variable you used, but you perfectly answered my question, thank you!  

---

