I'm more in the CS based stack exchange, but this question prompted me to come in here.

I've been compiling a large set of ephemerides for solar system, stars with mag > 6.8, exo planets etc, and I am now working on the DSO catalog.

The app actually holds celestial objects in 3D space, and I made conversions from RA/DEC/dist(parsec) for various objects, but I am having trouble with DSO objects.

I know of a red shift time base formula, but heard the conversion is not very good. Also, I understand that most estimations cannot be counted as precise, but I would like to have these objects within 3D space.

Can anyone tell me what features I should look for in a catalog and what formula I can base myself on for this conversion, if any?



1 Answer 1


There are many cosmological distance measures and what you need depends on what you want to do. If you want to position the object in 3D space where it is today, you need its proper distance. If you want to e.g. display the object with a certain angular size on the sky, and you want to figure that size out from how far away the object is, you need the angular diameter distance.

To calculate any of the measures, you need the object's redshift $z$. You will probably need to store the comoving distance (= proper distance today) and redshift so that you can convert to other distance measures quickly without redoing the integral.

  • $\begingroup$ So does this mean there is no way to get the distance from other features (ie red shift, and some other variable)? None of the catalogs actually have distance $\endgroup$
    – triple7
    Sep 27, 2018 at 23:08
  • $\begingroup$ You can get any of the distance measures from the redshift and an assumed cosmology (which tells you the parameters Omega). On the linked page, you find the function $E(z)$, which you will need to integrate to get the comoving distance. The other distance measures can then be computed from that and the redshift. $\endgroup$
    – user18746
    Sep 27, 2018 at 23:14

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