Latest version of my model based on the above tweaks.

I am delighted to see how well the molecular cloud distribution seems to track my model (although other people may disagree).

Moreover, these map experiments provide strong hints where to look in the Gaia DR4 data to try to find galactic structure.

Combined with Gaia OB star density, masers (light blue dots) and structures from my spiral model including the bar, ring, Carina arm (green) and Norma arm (blue).

I'm continuing to tweak my model of the Milky Way based on catalogs of objects in or near the galactic plane. I found a great molecular cloud catalog described in a 2017 paper.

https://ui.adsabs.harvard.edu/abs/2017ApJ...834...57M/abstract

Although distance estimates derived from gas velocity are not as reliable as parallax, we are still dependent on them because there are very few maser parallax measurements from the southern hemisphere.

This shows the molecular cloud data and my model out to 12 kpc. Galactic centre down.

My wife loves #chocolates and #boardgames so for Valentine's Day I got her a box of Belgian pralines and we played a round of Star Realms. Blowing up each other's galactic bases may not have *quite* fit the theme of the day but was fun. I squeeked to victory with 11 authority points remaining.

Slight tweak.

Curiously, it seems that the data has been converging to consistent positions. What is not converging is the spiral models. So arguably not really about science but how you want to represent the data.

More details over here: https://bsky.app/profile/galaxymap.bsky.social/post/3meikzx3ws22r

My latest Milky Way model.

RE: https://mastodon.world/@anttipeltola/116033889455944114

I don't understand this thread. Replacing Facebook would be quite easy technically. There are several existing software packages that could replicate the core functionality. The issue is social not technical. Outside the university everyone would remain on Facebook and even inside the university there would be resistance to change.

For reference, here is my full model rotated so that the galactic centre is down. The dashed circle shows the outer limit of most Gaia data in the galactic plane.

Just for fun, here is the above image with my two-armed model of the Milky Way: Carina arm (green) and Norma arm (blue).

Of course there is no consensus on the structure of the Milky Way so this is just my model.

@minzastro Good point. The map is not the image.

The radius of the above image is 12 kpc.

Sadly there is almost no data available on the parallaxes of masers visible from the southern hemisphere. A big block to creating more reliable maps of the Milky Way.

HII regions paper: https://ui.adsabs.harvard.edu/abs/2025A%26A...696A..67S/abstract

OB star paper: https://ui.adsabs.harvard.edu/abs/2025MNRAS.543...63P/abstract

We don't know for *sure* that the Milky Way has such a prominent inner ring but several papers have proposed it.

One of the best ways to map the Milky Way is to combine multiple data sets covering different parts of the galactic plane.

This image has masers (blue), estimated bar and ring positions, a new catalog of about 500 HII regions with Gaia-derived distances (red), star density from a new OB star catalog and part of figure 6 from the OB star paper showing individual stars with low error distances.

The dashed line shows a circle with radius 6 kpc. Almost all Gaia data in the galactic plane appears within this circle. Orange is the inner ring, red the bar, and blue the two spiral arms. I sometimes call this a fiddler crab model since one arm is much larger than the other. (Image: NOAA)

As always I should note that there is no consensus on the structure of the Milky Way. This is my personal model.