Interesting object~ how do I tell the distance apart?

https://www.legacysurvey.org//viewer/?ra=159.2657&dec=20.4366&layer=ls-dr9&zoom=13

I am pretty sure these 2 galaxies aren’t near each other (just overlapping) but how do I actually check?

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In this case it is fairly easy; just go to Overlays > -Spectroscopy > SDSS Spectra

You then get the redshift (z) for both galaxies; z=0.042 & z=0.043

This is not exactly the same value but I suspect it is close enough for interaction. Although I’m not seeing any signs of that (disturbances and such).

Otherwise you’ll have to go to SIMBAD for both galaxies to get the redshift z there. If there is no redshift available it becomes a ‘guessing game’.

Hope this helps :slight_smile:

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yes very helpful thank you

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If you calculate distance
yellow is 566 million light-years away
blue is 579 million light-years away

So, about 13 million light-year apart

Milky Way and Andromeda are about 2 million light-years apart, and are not interacting.

So, too far apart for interaction.

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Thank you Christine, very helpful!

(EDIT although Wolfram Apha only seems to mention the redshift, not assumed distance)

I’ll try again.
i can’t seem to copy the address bar.
So you’ll have to enter 0.042 from this page.
I have to keep hitting the “cosmological redshift” button to make it work

Input information
cosmological redshift |
redshift | 0.42
Cosmological results
time ago (lookback time) | 4.44 billion years
time since big bang | 9.27 billion years
distance (comoving) | 5.29 billion ly (light years)
1620 Mpc (megaparsecs)
5×10^22 km (kilometers)
3.11×10^22 miles
fraction of total observable radius | 0.113
scale factor | 0.704 × current value
epoch | matter dominated, post-recombination
radiation temperature | 3.87 K (kelvins)
(based on 5-year WMAP data and Lambda-CDM model; current universe age: 13.7 billion years)
Timeline
Timeline
Visible spectrum shift
Visible spectrum shift

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thank you!