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Comment by -warren | Hacker News Reader

Counter-rotating spiral galaxies. Super neat! https://skyviewer.app/embed?target=186.66721+8.89072&fov=0.2...

> "?target=186.66721+8.89072"

(For those who haven't noticed, you can just simply paste 186.66721+8.89072 or whichever target you're curious about in an astronomy database like Aladin[0], and there right-click on "What is this?")

[0] https://aladin.cds.unistra.fr/AladinLite/?target=12%2026%204...

I wonder if there's some kind of gravitational lensing going on. A lot of the galaxies look similar, but in different orientations.

https://skyviewer.app/embed?target=186.66721+8.89072&fov=0.2...

https://skyviewer.app/embed?target=185.46019+4.48014&fov=0.6...

https://skyviewer.app/embed?target=188.49629+8.40493&fov=1.3...

(Quick side note, if you go to /explorer instead of /embed you can zoom out so you can see the whole image at once)

https://skyviewer.app/explorer?target=187.69717+12.33897&fov...

That is interesting!

They look like they're roughly in the same plane. Is it safe to assume they're roughly in the same plane, or could they be really distant along the line of sight? The similarity in size makes me think they are, but I don't have any reason to be confident in that judgment.

Those are NGC 4411 a+b and they're indeed right next to each other,

https://noirlab.edu/public/images/iotw2421b/ ("thought to be right next to each other — both at a distance of about 50 million light-years")

What's going on directly above with what looks to be 3-4 galaxies interacting?

It says that NGC 4410 is (gravitationally) interacting galaxies. After clicking through the link, it calls it RSCG 55 instead and explains more. I don't understand the naming scheme.

The naming scheme is based on the principle "tens of thousand of people have done this over thousands of years, and they all named things themselves". Its not uncommon for objects to have ~20 separate names[1], with some having over a hundred [2].

In this particular case, RSCG 55 means a group of galaxies[3], of which NGC 4410 is one member. Apparently RSCG is the "Redshift Survey Compact Groups" (https://cds.unistra.fr/cgi-bin/Dic-Simbad?RSCG) so 55 is just an index number.

That's also the case for the 4410 after NGC; in that case stands for "New General Catalog". In contrast the Sloan Digital Sky Survey gave NGC 4410 the name SDSS J122628.29+090111.4 where the numbers indicates its position in the sky.

The "index number" and the "position of the sky" are the two most popular naming strategies.

[1] NGC 4410 has 37, but the NGC objects are among the more popular https://simbad.u-strasbg.fr/simbad/sim-id?Ident=+NGC+4410&Nb... [2] https://simbad.u-strasbg.fr/simbad/sim-id?Ident=M87&submit=s... [3] https://simbad.u-strasbg.fr/simbad/sim-id?Ident=RSCG+55&NbId...

"like NGC 4410, above them in this image. The four interacting galaxies of that system are connected by tidal bridges, created by the gravity of each galaxy pulling on the others in the system."

Dang. I think I got terminology blinded by the time I got there.

I believe there would be a difference in their red/blue signatures if they were moving relative to each other, but as you say they clearly are on the same plane

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