<p>It is very difficult to measure Galactic orbital speeds of stars in our galaxy for several reasons.  We are moving with them and do not have a reliable measurement yet of even our own orbital motion. We only get one component of motion, the radial component (although Gaia is about to change that).  Dust in the galactic plane prevents us from seeing very far in our own galaxy.  So, when we measure Dark Matter in galaxies, it usually done in other galaxies where we can see both sides of the galaxy and, except for inclination angle, directly measure the orbital motion.  </p>

CC BY-SA 4.0
2018-05-15T22:44:32.000Z
Can you give a citation of such work for a suitable galaxy?
Steve Linton
CC BY-SA 4.0
2018-08-14T03:13:48.743Z
I'm okay with other galaxies. I was looking for data that could be used to calculate dark matters effect, so if that involved data from other galaxies that is perfect.
Ben Kushigian
CC BY-SA 3.0
2018-04-15T21:01:01.490Z
2018-04-15T21:01:01.490Z
eshaya
<p>I don't know of any sources for the data you're looking for, however, I did something like this a year ago in one of my classes. An option would be (keeping in mind that you don't want to be too rigorous) to get an image of a <em>good enough</em> galaxy, i.e a fits file released to the public like <a href="https://www.eso.org/public/images/eso9949a/?lang" rel="nofollow noreferrer">M83</a>. Under the assumption that wherever there's light there's mass (mass = $kL$, where $k$ is a constant and $L$ luminosity), you can equate forces and solve for velocity. This would get you values for "expected virtual velocities" at each radii, so you could plot the data and get a curve with a certain shape.  What you expect to find is that as you increase radii, the values for velocity drop under the initial assumption. Then you go and <em>compare</em> with different and more rigorous measurements, like <a href="http://www.astro.ucla.edu/~lucian/papers/m83.co.pdf" rel="nofollow noreferrer">this one</a> (page 18). Here you notice that the curve doesn't quite agree with the shape of the curve you got from the image, since it peaks and stays approximately constant (as opposed to dropping). Why is that? Maybe there's <em>something</em> that light can't show you.
Note: as I said, this isn't rigorous. I've skipped conversion from counts per pixel, relationship between flux and luminosity and some other things. I've also assumed that you can work with something like astropy to process the data. Hope it helps</p>

CC BY-SA 4.0
2018-08-15T01:12:46.553Z
2018-08-15T01:12:46.553Z
Solfreludio
<p>I'm trying to find some data that I can use to derive dark matter (in a loosey-goosey sort of way, I won't be too rigorous). I'm helping a friend out with a final project for his astronomy course and I'm tasked with doing the maths. Any idea where I can find a table of various stars distance from the center of our galaxy and their speed (how fast they are going around the center of the galaxy)? This does not need to be comprehensive but would ideally contain several data sources from various representative radii. Also some sort of formatted text would be SUPER cool so I could just tell my computer to do the calculations!</p>

CC BY-SA 4.0
2018-08-14T03:01:04.923Z
Related article:   http://www.slate.com/blogs/bad_astronomy/2014/03/25/galactic_rotation_astronomers_use_hubble_to_measure_stars_motions.html
userLTK
<dark-matter><data-analysis>
Deriving Dark Matter; specifically looking for a table of stellar speed versus distance from center of galaxy to derive dark matter
Ben Kushigian
# Deriving Dark Matter; specifically looking for a table of stellar speed versus distance from center of galaxy to derive dark matter

(Asked by: username_0 on 2014-12-12)

I'm trying to find some data that I can use to derive dark matter (in a loosey-goosey sort of way, I won't be too rigorous). I'm helping a friend out with a final project for his astronomy course and I'm tasked with doing the maths. Any idea where I can find a table of various stars distance from the center of our galaxy and their speed (how fast they are going around the center of the galaxy)? This does not need to be comprehensive but would ideally contain several data sources from various representative radii. Also some sort of formatted text would be SUPER cool so I could just tell my computer to do the calculations!

**Tags:** dark-matter, data-analysis
> **Comments:**
> **username_1**: Related article:   http://www.slate.com/blogs/bad_astronomy/2014/03/25/galactic_rotation_astronomers_use_hubble_to_measure_stars_motions.html  

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## 2 answers

### Answer by username_2 on 2018-04-15. Score: 2

It is very difficult to measure Galactic orbital speeds of stars in our galaxy for several reasons. We are moving with them and do not have a reliable measurement yet of even our own orbital motion. We only get one component of motion, the radial component (although Gaia is about to change that). Dust in the galactic plane prevents us from seeing very far in our own galaxy. So, when we measure Dark Matter in galaxies, it usually done in other galaxies where we can see both sides of the galaxy and, except for inclination angle, directly measure the orbital motion.

> **Comments:**
> **username_3**: Can you give a citation of such work for a suitable galaxy?  
> **username_0**: I'm okay with other galaxies. I was looking for data that could be used to calculate dark matters effect, so if that involved data from other galaxies that is perfect.  

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### Answer by username_4 on 2018-08-15. Score: 2

I don't know of any sources for the data you're looking for, however, I did something like this a year ago in one of my classes. An option would be (keeping in mind that you don't want to be too rigorous) to get an image of a *good enough* galaxy, i.e a fits file released to the public like [M83](https://www.eso.org/public/images/eso9949a/?lang). Under the assumption that wherever there's light there's mass (mass = $kL$, where $k$ is a constant and $L$ luminosity), you can equate forces and solve for velocity. This would get you values for "expected virtual velocities" at each radii, so you could plot the data and get a curve with a certain shape. What you expect to find is that as you increase radii, the values for velocity drop under the initial assumption. Then you go and *compare* with different and more rigorous measurements, like [this one](http://www.astro.ucla.edu/~lucian/papers/m83.co.pdf) (page 18). Here you notice that the curve doesn't quite agree with the shape of the curve you got from the image, since it peaks and stays approximately constant (as opposed to dropping). Why is that? Maybe there's *something* that light can't show you.
Note: as I said, this isn't rigorous. I've skipped conversion from counts per pixel, relationship between flux and luminosity and some other things. I've also assumed that you can work with something like astropy to process the data. Hope it helps


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