Galaxy Map
@galaxymap.bsky.social
The first accurate and detailed maps of the Milky Way and ways to promote and visualize them (including VR).
Website: https://kevinjardine.dev
Tip jar: https://tiptopjar.com/kevinjardine
Also follow me on @galaxy_map@mastodon.social
Website: https://kevinjardine.dev
Tip jar: https://tiptopjar.com/kevinjardine
Also follow me on @galaxy_map@mastodon.social
Pinned
Galaxy Map
@galaxymap.bsky.social
· Jan 8
The Phantom Arm
Can Gaia DR4 improve our maps of the inner galaxy?
kevinjardine.dev
I've put up one of the most ambitious (and lengthy) articles I've written on the Milky Way. The timing works out well because this year is the 75th anniversary of the detection of the 21 cm line, one of the events that started the Golden Age of galactic cartography.
kevinjardine.dev/blog/post-16/
kevinjardine.dev/blog/post-16/
I will work on an image using this catalog without the race tracks.
February 13, 2026 at 5:07 PM
I will work on an image using this catalog without the race tracks.
Figure 10 has a great map. Yes it is based on dubious velocity->distance conversions but it shows interesting patterns. It also makes a point that I've often made, which is that astronomers often insist on overlaying four arm spiral models on maps that seem to provide little evidence for them.
February 13, 2026 at 4:57 PM
Figure 10 has a great map. Yes it is based on dubious velocity->distance conversions but it shows interesting patterns. It also makes a point that I've often made, which is that astronomers often insist on overlaying four arm spiral models on maps that seem to provide little evidence for them.
All the multicelluar eukaryotic organisms like animals, plants and fungi, descend from Archaea.
February 12, 2026 at 9:56 AM
All the multicelluar eukaryotic organisms like animals, plants and fungi, descend from Archaea.
Biology gives us another example in the "domains" of life. The more we know, the more complex we realize life is but paradoxically that can lead to simpler models. Recently there has been a trend towards a model with only two domains: Bacteria and Archaea.
February 12, 2026 at 9:55 AM
Biology gives us another example in the "domains" of life. The more we know, the more complex we realize life is but paradoxically that can lead to simpler models. Recently there has been a trend towards a model with only two domains: Bacteria and Archaea.
Having said all this, I also like the game of discerning the tea leaves and trying to model the large scale structure of the Milky Way from the limited data available. Especially with the expected Gaia DR4 release in December.
February 12, 2026 at 8:56 AM
Having said all this, I also like the game of discerning the tea leaves and trying to model the large scale structure of the Milky Way from the limited data available. Especially with the expected Gaia DR4 release in December.
The argument about how many spiral arms the Milky Way has is similarly much more about cartographic aesthetics than science. I prefer a two arm model of the Milky Way over a five arm model primarily because I prefer simpler models, not because I have different data.
February 12, 2026 at 8:48 AM
The argument about how many spiral arms the Milky Way has is similarly much more about cartographic aesthetics than science. I prefer a two arm model of the Milky Way over a five arm model primarily because I prefer simpler models, not because I have different data.
So arguably this list really contains three continents and one large island. There is no way to resolve this question scientifically because continents, like spiral arms, are models we use for maps rather than real objects.
February 12, 2026 at 8:43 AM
So arguably this list really contains three continents and one large island. There is no way to resolve this question scientifically because continents, like spiral arms, are models we use for maps rather than real objects.
Traditionally we list seven continents: Europe, Asia, Africa, North America, South America, Antarctica and Australia. But really this list is pretty arbitrary. Europe, Asia and Africa form a single connected land mass as do the Americas. Australia is much smaller than the other continents.
February 12, 2026 at 8:38 AM
Traditionally we list seven continents: Europe, Asia, Africa, North America, South America, Antarctica and Australia. But really this list is pretty arbitrary. Europe, Asia and Africa form a single connected land mass as do the Americas. Australia is much smaller than the other continents.
This is partly because I am not convinced that we have enough reliable data over a large enough region to convincingly locate spiral arms but there is another reason: spiral arms are really human constructs like continents that we use to label large scale maps and not necessarily real objects.
February 12, 2026 at 8:31 AM
This is partly because I am not convinced that we have enough reliable data over a large enough region to convincingly locate spiral arms but there is another reason: spiral arms are really human constructs like continents that we use to label large scale maps and not necessarily real objects.
Normally my maps of the Milky Way focus on specific objects (star clusters, HII regions), or density distributions (dust, hot stars). I sometimes extrapolate beyond these to larger OB associations or star formation regions (eg. Ori OB1) but very rarely do I try to discern spiral arms.
February 12, 2026 at 8:25 AM
Normally my maps of the Milky Way focus on specific objects (star clusters, HII regions), or density distributions (dust, hot stars). I sometimes extrapolate beyond these to larger OB associations or star formation regions (eg. Ori OB1) but very rarely do I try to discern spiral arms.
Of course the Milky Way has a larger more prominent bar (and possibly ring).
February 11, 2026 at 12:25 PM
Of course the Milky Way has a larger more prominent bar (and possibly ring).
ESA'S Euclid mission view.
February 11, 2026 at 12:23 PM
ESA'S Euclid mission view.
PHANGS (phangs.org) has several interesting images of IC 342.
February 11, 2026 at 12:07 PM
PHANGS (phangs.org) has several interesting images of IC 342.
Compare with my latest model.
February 11, 2026 at 11:33 AM
Compare with my latest model.
Also shows the huge difference between a model and the chaos and complexity of a real barred spiral galaxy.
February 11, 2026 at 11:29 AM
Also shows the huge difference between a model and the chaos and complexity of a real barred spiral galaxy.
If IC 342 was the Milky Way, this image shows the approximate location of the Sun surrounded by the region we can visualize in the galactic plane (dashed circle) using Gaia. It shows the impossible challenge of determining the galactic structure from the Gaia data alone.
February 11, 2026 at 11:22 AM
If IC 342 was the Milky Way, this image shows the approximate location of the Sun surrounded by the region we can visualize in the galactic plane (dashed circle) using Gaia. It shows the impossible challenge of determining the galactic structure from the Gaia data alone.
This even has two differently sized spiral arms like my Milky Way model.
February 11, 2026 at 11:03 AM
This even has two differently sized spiral arms like my Milky Way model.
Love this image of IC 342.
Credit: Credit: NASA/JPL-Caltech/J. Turner (UCLA)
Credit: Credit: NASA/JPL-Caltech/J. Turner (UCLA)
February 11, 2026 at 11:02 AM
Love this image of IC 342.
Credit: Credit: NASA/JPL-Caltech/J. Turner (UCLA)
Credit: Credit: NASA/JPL-Caltech/J. Turner (UCLA)
Although various sources call NGC 3344 "intermediate", "weakly barred", "non-barred" so obviously the bar is not so clear.
February 11, 2026 at 9:13 AM
Although various sources call NGC 3344 "intermediate", "weakly barred", "non-barred" so obviously the bar is not so clear.
NGC 3344 is also a nice barred spiral galaxy with observations finding both an inner and outer ring.
apod.nasa.gov/apod/ap25060...
apod.nasa.gov/apod/ap25060...
APOD: 2025 June 8 – Facing NGC 3344
A different astronomy and space science
related image is featured each day, along with a brief explanation.
apod.nasa.gov
February 11, 2026 at 9:03 AM
NGC 3344 is also a nice barred spiral galaxy with observations finding both an inner and outer ring.
apod.nasa.gov/apod/ap25060...
apod.nasa.gov/apod/ap25060...
Messier 109 is quite a nice barred spiral. No obvious ring, but Wikipedia says that it does have a weak ring in fact.
Credit: KPNO/NOIRLab/NSF/AURA/George Hatfield and Flynn Haase
Credit: KPNO/NOIRLab/NSF/AURA/George Hatfield and Flynn Haase
February 11, 2026 at 8:47 AM
Messier 109 is quite a nice barred spiral. No obvious ring, but Wikipedia says that it does have a weak ring in fact.
Credit: KPNO/NOIRLab/NSF/AURA/George Hatfield and Flynn Haase
Credit: KPNO/NOIRLab/NSF/AURA/George Hatfield and Flynn Haase
Along with Messier 109, Messier 98, Messier 106, Messier 95, Messier 91 (which I put up yesterday), and Messier 31 (Andromeda) I believe that these are the nine barred spiral galaxies in the Messier catalog. But the definition of a bar is a little vague so I might have missed some.
February 11, 2026 at 8:40 AM
Along with Messier 109, Messier 98, Messier 106, Messier 95, Messier 91 (which I put up yesterday), and Messier 31 (Andromeda) I believe that these are the nine barred spiral galaxies in the Messier catalog. But the definition of a bar is a little vague so I might have missed some.
Messier 66. Beautiful bar and spiral arms. No obvious ring. Credit: ESO.
February 11, 2026 at 8:20 AM
Messier 66. Beautiful bar and spiral arms. No obvious ring. Credit: ESO.
Messier 61. This one does seem to have an inner ring.
Credit: ESA/Hubble & NASA
Credit: ESA/Hubble & NASA
February 11, 2026 at 8:15 AM
Messier 61. This one does seem to have an inner ring.
Credit: ESA/Hubble & NASA
Credit: ESA/Hubble & NASA