How can someone obtain such vector, for stars in the Milky Way?

Input should be star data (from a catalog, eg: Hipparcos) and Julian Date.

Output should be a Vector Position (in pc) in relation to the galactic center.

  • $\begingroup$ A vector position requires a reference axis set as well as a central point. What do you propose to use as to define the reference with. $\endgroup$ Jan 14, 2016 at 0:02
  • $\begingroup$ Presumably the galactic coordinate system (en.wikipedia.org/wiki/Galactic_coordinate_system) $\endgroup$
    – user21
    Jan 14, 2016 at 0:16
  • $\begingroup$ As stated, the axis center should be set on the Galactic Center (center of the Milky Way). Galactic Coordinates alone aren't enough to answer this question. I need to know how to transform the input data (star data and date) into the required position vector. $\endgroup$
    – hawaii
    Jan 14, 2016 at 0:38
  • $\begingroup$ I'm not sure if this is helpful or not, but this paper (pdf) details how to transform between different coordinate systems. $\endgroup$ Jan 14, 2016 at 9:19
  • $\begingroup$ It could be possible, but from the data available on sites like Sinbad it appears that distant stars have more data to the used on the calculation, than a simple horizontal coordinate system (where you would include the required date) to galactic coordinate system transformation. $\endgroup$
    – hawaii
    Jan 14, 2016 at 13:36

1 Answer 1


EDIT: It turns out a major problem with galaxy-center-based coordinates is that we don't actually know how far from us the center of the galaxy actually is. According to https://en.wikipedia.org/wiki/Galactic_Center estimates vary between 24,800 and 28,400 light years. You could arbitrarily choose a value, but the results would be off by at least 2,000 light years in some cases.

I was surprised that I couldn't find something like this online directly. The closest I found is the file "heasarc_tycho2.tdat.gz" on http://heasarc.nasa.gov/FTP/heasarc/dbase/dump/

The format is explained on http://heasarc.nasa.gov/W3Browse/all/tycho2.html and it includes the galactic latitude and longitude which are explained here:


Using this information, you'd still have to compute the positions yourself, but at least all of the data is there.

Of course, as others have noted, you can take any star catalog with any set of coordinates and convert it to the format you need. The catalog I list above just makes it a little easier, since they're precomputed some of the steps for you.

As you mention above, SIMBAD also includes galactic coordinates, but I couldn't find an easy way to download the entire catalog.

  • $\begingroup$ Just read your edit. Our goal is just to estimate star movements around the galaxy and plot them in 3D for scientific disclosure. Very precise scientific accuracy would be a plus, but it is not really required. $\endgroup$
    – hawaii
    Jan 15, 2016 at 3:43
  • $\begingroup$ For that, wouldn't you just need the proper motion of stars? $\endgroup$
    – user21
    Jan 15, 2016 at 4:39
  • $\begingroup$ I dont really know. This issue began when I was asked to create a 3D plot of the two star 'orbits' mentioned in this article. In the article they dont use proper motion. $\endgroup$
    – hawaii
    Jan 15, 2016 at 12:13

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