<p>I don't know if this will be closed as too general, but I think there's a fun question in here about galaxy mapping.</p>

<p>The trick is to have a good map of the galaxy.   We can't see large sections of the Milky way, so we might have a better map of Andromeda than the Milky way overall from our perspective.   </p>

<p>And yes, there are landmarks.    <a href="https://en.wikipedia.org/wiki/Pioneer_plaque" rel="nofollow noreferrer">Pioneer</a> and <a href="https://en.wikipedia.org/wiki/Voyager_Golden_Record" rel="nofollow noreferrer">Voyager</a> used Pulsars as landmarks in a diagram on their plaques.</p>

<p><a href="https://i.sstatic.net/aXySa.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/aXySa.jpg" alt="http://news.nationalgeographic.com/content/dam/news/2017/08/14/voyager-pulsar-map/pulsar-map-voyager.ngsversion.1502807521895.adapt.1900.1.jpg"></a></p>

<p>There are <a href="http://www.oarval.org/pulsars.htm" rel="nofollow noreferrer">by this estimate</a>, at least 200,000 pulsars in the milky-way.  A map of 14 of them won't do someone on the other side of the galaxy if our map has some errors (<a href="https://www.forbes.com/sites/startswithabang/2017/08/17/voyagers-cosmic-map-of-earths-location-is-hopelessly-wrong/#60c130dd69d5" rel="nofollow noreferrer">which Voyager's might</a>) or if they don't have a good chart on the other side of the galaxy.  <a href="https://en.wikipedia.org/wiki/Pulsar#Maps" rel="nofollow noreferrer">Pulsars are very precise</a> and they can make  very landmarks if you have enough of them and properly spaced.   </p>

<p>Also, stars move, so maps age and lose accuracy over time, but in your star-wars example, a human lifetime wouldn't change things much.</p>

<p>Other possible landmarks include X-ray binaries,  very large stars (less common than smaller ones), black holes, neutron stars, the age of stars could be used, contact binaries, nebulas (or is that nebulae), stellar nurseries.   Identifying an individual planet would be easy given good data and a complete map.   A typical modern computer could do it, but the trick is having a good map.   There's about 100 billion stars in the Milky way, so it comes down to how good the map is, but you're correct, if the small map is good, R2's larger galaxy map is irrelevant.   To be relevant, the smaller map should have been maybe 100-500 stars and R2's map nearly the entire galaxy, and there would be ways to make the map useless if it fell into enemy hands, by not including pulsars or star size, making it very very difficult to identify which part of the galaxy by just 100 stars, none of them distinct.   The principal of needing both maps is valid and could be done, but you're right that the size of the 2nd map was ridiculous, also, why would they need to track his journey like in the picture?.    Movies often ignore the finer points like that and just focus on what looks cool.</p>

CC BY-SA 3.0
2017-10-05T04:44:13.193Z
Why do you think the smaller map should have 100-500 stars?
Sebastian
CC BY-SA 3.0
2017-10-05T06:04:40.250Z
@Sebastian I picked those numbers off the top of my head.  I wanted enough where there were too many star systems to search one at a time (maybe 100 is too few), but beyond that, my main point was that the 2nd map in star wars was way too large - as you suggested.
userLTK
CC BY-SA 3.0
2017-10-03T22:35:43.560Z
2017-10-03T22:35:43.560Z
userLTK
<p>I am wondering why it was so hard to locate Luke in Star Was Episode 7, if you already have the small part of the map.</p>

<p>Suppose we have a sector of <em>our</em> galaxy that roughly equals the one missing in this <a href="http://ko.starwars.wikia.com/wiki/%EC%9D%80%ED%95%98%EA%B3%84?file=TFA_galaxy_map.jpg" rel="nofollow noreferrer">image</a>. (I found no image on the web of the part in question. In the movie version on netflix you can take good look at it at 52:56.) </p>

<p>Is it possible and how hard would it be to identify a planet within that part of the map, given our knowledge of our galaxy and</p>

<ol>
<li>we only know the small part and have no information about its size.</li>
<li>there might be "landmarks" (planets, stars, nebulars, and the like) missing.</li>
</ol>

<p>If it is not possible, what minimum requirements would have to be met (on the available equipment, the map, our knowledge, ..) to make it possible?</p>

<p>Please note: this is not a Star Wars question, that is just the motivation.</p>

<p>About which galaxies do we have enough knowledge to be able to do this?</p>

<p><a href="http://ko.starwars.wikia.com/wiki/%EC%9D%80%ED%95%98%EA%B3%84?file=TFA_galaxy_map.jpg" rel="nofollow noreferrer">http://ko.starwars.wikia.com/wiki/%EC%9D%80%ED%95%98%EA%B3%84?file=TFA_galaxy_map.jpg</a></p>

CC BY-SA 3.0
2017-10-04T02:40:45.777Z
This really sounds like a computational problem : fuzzy 3D pattern matching with error bounds.  Given we could be talking about billions of stars to match we'd probably be relying on a probabilistic match of a sample of the best data.  Nothing a civilization that could accurately map star positions and characteristics could not match.  We could probably do it for the Milky Way, except I think the accuracy of the data on positions might be problematic - i.e. vastly increase computation time.
StephenG - Help Ukraine
CC BY-SA 3.0
2017-10-04T05:13:58.913Z
In Cixin Liu's "Remembrance of Earth's Past" trilogy, one of the plot point revolves around messages with coordinates to a particular star.  I can't remember exactly what form the coordinates took, but it was basically a 3D map showing the distances to nearby stars.
Phiteros
CC BY-SA 3.0
2017-10-04T13:16:22.473Z
I'm voting to close this question as off-topic because this belongs on WorldBuilding.SE, being a SciFi/fantasy question
Carl Witthoft
CC BY-SA 3.0
2017-10-04T13:18:20.577Z
Further, this is a map / matching problem which really has nothing to do with astronomy or cosmology.  You might as well as how to identify Luke with a partial fingerprint (assuming humanoids in a galaxy far away had fingerprints)
Carl Witthoft
CC BY-SA 3.0
2017-10-04T14:58:14.433Z
Why not ask in [SciFi Stackexchange](https://scifi.stackexchange.com/) instead? There are plenty of astro-knowledgeable people there who are also interested in the in-universe applications. For example [Did they ever deal with non-relativistic kinematics on Dragon's Egg?](https://scifi.stackexchange.com/q/155063/51174).
uhoh
CC BY-SA 3.0
2017-10-05T04:55:26.900Z
This intends to be a question about the state of the art star mapping and knowledge, which imho belongs to astronomy. The mentioned fantasy is just the motivation.(As I already stated.) I am also not interested in any reasons possible in a science fiction universe, wether created by myself or somebody else. It is really more in the sense of "Where are we today?". And where would the astro-knowledgeable people go to answer their questions? So I figured I'd keep the ways short.
Sebastian
<galaxy><milky-way><observable-universe>
Find a planet with incomplete information of a star chart
Sebastian
# Find a planet with incomplete information of a star chart

(Asked by: username_0 on 2017-10-03)

I am wondering why it was so hard to locate Luke in Star Was Episode 7, if you already have the small part of the map.

Suppose we have a sector of *our* galaxy that roughly equals the one missing in this [image](http://ko.starwars.wikia.com/wiki/%EC%9D%80%ED%95%98%EA%B3%84?file=TFA_galaxy_map.jpg). (I found no image on the web of the part in question. In the movie version on netflix you can take good look at it at 52:56.)

Is it possible and how hard would it be to identify a planet within that part of the map, given our knowledge of our galaxy and

1. we only know the small part and have no information about its size.
2. there might be "landmarks" (planets, stars, nebulars, and the like) missing.

If it is not possible, what minimum requirements would have to be met (on the available equipment, the map, our knowledge, ..) to make it possible?

Please note: this is not a Star Wars question, that is just the motivation.

About which galaxies do we have enough knowledge to be able to do this?

<http://ko.starwars.wikia.com/wiki/%EC%9D%80%ED%95%98%EA%B3%84?file=TFA_galaxy_map.jpg>

**Tags:** galaxy, milky-way, observable-universe

> **Comments:**
> **username_1**: This really sounds like a computational problem : fuzzy 3D pattern matching with error bounds.  Given we could be talking about billions of stars to match we'd probably be relying on a probabilistic match of a sample of the best data.  Nothing a civilization that could accurately map star positions and characteristics could not match.  We could probably do it for the Milky Way, except I think the accuracy of the data on positions might be problematic - i.e. vastly increase computation time.  
> **username_2**: In Cixin Liu's "Remembrance of Earth's Past" trilogy, one of the plot point revolves around messages with coordinates to a particular star.  I can't remember exactly what form the coordinates took, but it was basically a 3D map showing the distances to nearby stars.  
> **username_3**: I'm voting to close this question as off-topic because this belongs on WorldBuilding.SE, being a SciFi/fantasy question  
> **username_3**: Further, this is a map / matching problem which really has nothing to do with astronomy or cosmology.  You might as well as how to identify Luke with a partial fingerprint (assuming humanoids in a galaxy far away had fingerprints)  
> **username_4**: Why not ask in [SciFi Stackexchange](https://scifi.stackexchange.com/) instead? There are plenty of astro-knowledgeable people there who are also interested in the in-universe applications. For example [Did they ever deal with non-relativistic kinematics on Dragon's Egg?](https://scifi.stackexchange.com/q/155063/51174).  
> **username_0**: This intends to be a question about the state of the art star mapping and knowledge, which imho belongs to astronomy. The mentioned fantasy is just the motivation.(As I already stated.) I am also not interested in any reasons possible in a science fiction universe, wether created by myself or somebody else. It is really more in the sense of "Where are we today?". And where would the astro-knowledgeable people go to answer their questions? So I figured I'd keep the ways short.  

---

## 1 answers

### Answer by username_5 on 2017-10-03. Score: 2 | Accepted answer

I don't know if this will be closed as too general, but I think there's a fun question in here about galaxy mapping.

The trick is to have a good map of the galaxy. We can't see large sections of the Milky way, so we might have a better map of Andromeda than the Milky way overall from our perspective.

And yes, there are landmarks. [Pioneer](https://en.wikipedia.org/wiki/Pioneer_plaque) and [Voyager](https://en.wikipedia.org/wiki/Voyager_Golden_Record) used Pulsars as landmarks in a diagram on their plaques.

[![http://news.nationalgeographic.com/content/dam/news/2017/08/14/voyager-pulsar-map/pulsar-map-voyager.ngsversion.1502807521895.adapt.1900.1.jpg](https://i.sstatic.net/aXySa.jpg)](https://i.sstatic.net/aXySa.jpg)

There are [by this estimate](http://www.oarval.org/pulsars.htm), at least 200,000 pulsars in the milky-way. A map of 14 of them won't do someone on the other side of the galaxy if our map has some errors ([which Voyager's might](https://www.forbes.com/sites/startswithabang/2017/08/17/voyagers-cosmic-map-of-earths-location-is-hopelessly-wrong/#60c130dd69d5)) or if they don't have a good chart on the other side of the galaxy. [Pulsars are very precise](https://en.wikipedia.org/wiki/Pulsar#Maps) and they can make very landmarks if you have enough of them and properly spaced.

Also, stars move, so maps age and lose accuracy over time, but in your star-wars example, a human lifetime wouldn't change things much.

Other possible landmarks include X-ray binaries, very large stars (less common than smaller ones), black holes, neutron stars, the age of stars could be used, contact binaries, nebulas (or is that nebulae), stellar nurseries. Identifying an individual planet would be easy given good data and a complete map. A typical modern computer could do it, but the trick is having a good map. There's about 100 billion stars in the Milky way, so it comes down to how good the map is, but you're correct, if the small map is good, R2's larger galaxy map is irrelevant. To be relevant, the smaller map should have been maybe 100-500 stars and R2's map nearly the entire galaxy, and there would be ways to make the map useless if it fell into enemy hands, by not including pulsars or star size, making it very very difficult to identify which part of the galaxy by just 100 stars, none of them distinct. The principal of needing both maps is valid and could be done, but you're right that the size of the 2nd map was ridiculous, also, why would they need to track his journey like in the picture?. Movies often ignore the finer points like that and just focus on what looks cool.

> **Comments:**
> **username_0**: Why do you think the smaller map should have 100-500 stars?  
> **username_5**: @username_0 I picked those numbers off the top of my head.  I wanted enough where there were too many star systems to search one at a time (maybe 100 is too few), but beyond that, my main point was that the 2nd map in star wars was way too large - as you suggested.  

---

