<p>The &quot;surface brightness&quot; of Andromeda will remain about the same. It will be roughly similar to the surface brightness of the Milky Way. From dark skies, the milky way is a lot more visible than you might think, but it won't be as bright as it can appear in long-exposure photographs.</p>

CC BY-SA 4.0
2024-11-25T06:28:48.560Z
2024-11-25T06:28:48.560Z
James K
<p>Once the Milkyway and the Andromeda Galaxy start to interact more intensely, Andromeda will become more and more like our own Milkyway. Of course one can make out some structure (like we do with light and dark dust clouds in front of or embedded in the Milkyway, with some directions offering more stars (towards our Galaxy's centre) and others less.</p>
<p>Overall, looking from the inside like we do, there will be more of a Milkyway (our current one extended by Andromeda), but it will basically look the same, possibly over more extended regions in the Sky as we might then have approximately two disks to look at which might be somewhat oblique to eachother with wild interactions mixing them gradually, all while we are sitting in one of the disks.</p>
<p>It's a wild mixing by cosmological standards - still it's a mostly collision-less interaction between the two galaxies when looking at the individual stars. The end result of a merger of spiral galaxies like both, Milkyway and Andromeda galaxy are, is considered to be an <a href="https://en.wikipedia.org/wiki/Elliptical_galaxy" rel="nofollow noreferrer">elliptical galaxy</a>. Yet that result will take far longer than our host star, the Sun, will exist. Both <a href="https://de.wikipedia.org/wiki/Whirlpool-Galaxie" rel="nofollow noreferrer">M51</a> and <a href="https://en.wikipedia.org/wiki/Antennae_Galaxies" rel="nofollow noreferrer">antenna galaxy</a> are examples of interacting galaxies which start to merge - and it might be an outside view of what the joint Milkyway and Andromeda Galaxy start to look like during the initial stages of merging (the antenna galaxies are more equal-sized, thus probably the better example).</p>
<p>Depending in where you place your observer after the merge is finished, you night sky might look a bit different than now when within an elliptical Galaxy which has a more 3D extent than the more or less flat spiral Galaxy; the clearly-defined band of the Milkyway as we know now might be missing with a hemisphere or larger region of the sky having more stars than the other when looking inward; the amount of Gas might also be less after the initial star burst has passed which happened during the actual merger - thus fewer dark and bright clouds like <a href="https://en.wikipedia.org/wiki/Bok_globule" rel="nofollow noreferrer">bok globules</a> or <a href="https://en.wikipedia.org/wiki/Orion_Nebula" rel="nofollow noreferrer">orion nebula</a>.</p>

CC BY-SA 4.0
2024-11-25T16:58:12.390Z
An actual merger between Andromeda and the MW will eventually produce something like an elliptical galaxy, and so *won't* "basically look the same".
Peter Erwin
CC BY-SA 4.0
2024-11-25T17:15:06.487Z
@PeterErwin eventually likely yes. Before that we will be in something nice as M51, the whirlpool galaxy, just more symmetrical. By then Earth is gone though :)
planetmaker
CC BY-SA 4.0
2024-11-25T20:51:03.003Z
No, it will look more like [the Antenna Galaxies](https://en.wikipedia.org/wiki/Antennae_Galaxies). Major mergers  don’t make for grand design spirals…
Peter Erwin
CC BY-SA 4.0
2024-11-27T06:07:50.860Z
@PeterErwin is right; the Milky Way is *currently* considered to have a well-defined structure, but the merger will completely obliterate it, definitely not maintain it.
4NT4R3S
CC BY-SA 4.0
2024-11-27T07:33:37.010Z
Allright. My consideration as described previously ended at the stage of contact, similar to what the image in the OP's posting shows. It's right that mergers usually are considered to create elliptical galaxies - and that might change the view after it is finished; I added that in another paragraph.
planetmaker
CC BY-SA 4.0
2024-11-25T09:34:46.240Z
2024-11-27T07:34:38.193Z
2024-11-27T07:34:38.193Z
planetmaker
<p>Galaxies are not singular points of light like stars are - they are diffuse, and emit light across their entire structure.</p>
<p>With that being said, you're correct in believing that Andromeda's shape would appear more vague to the naked eye, with a distinguishable core and a dim ellipse-like outer region.</p>
<p>You would only be able to replicate the image you provided by taking a long exposure picture of the night sky, but to the unaided eye you would see nowhere near that level of detail and color, simply because you're viewing the entire galaxy's light spread out over a large area.</p>

CC BY-SA 4.0
2024-11-25T15:04:38.383Z
2024-11-25T15:04:38.383Z
4NT4R3S
<p>First off, I have no expectation humans will be around to view this, and I know the earth will not be habitable 3.75 billion years from now.</p>
<p>This image from the <a href="https://science.nasa.gov/missions/hubble/nasas-hubble-shows-milky-way-is-destined-for-head-on-collision/" rel="noreferrer">science.nasa website</a> implies this is what could be seen in the night's sky at that time.
<a href="https://i.sstatic.net/rWv6qskZ.webp" rel="noreferrer"><img src="https://i.sstatic.net/rWv6qskZ.webp" alt="&quot;In this image, representing Earth's night sky in 3.75 billion years, Andromeda (left) fills the field of view...&quot; " /></a></p>
<p>Since the level of detail of the arm of the Milky Way Galaxy in this image doesn't represent what the naked eye can see, I assumed there is no chance details of the structure of Andromeda would be visible as well.</p>

<milky-way><night-sky><naked-eye><collision><andromeda>
Am I correct in assuming during the merger with the Milky Way the structure of the Andromeda Galaxy will not be visible to the naked eye?
Bob516
# Am I correct in assuming during the merger with the Milky Way the structure of the Andromeda Galaxy will not be visible to the naked eye?

(Asked by: username_0 on 2024-11-25)

First off, I have no expectation humans will be around to view this, and I know the earth will not be habitable 3.75 billion years from now.

This image from the [science.nasa website](https://science.nasa.gov/missions/hubble/nasas-hubble-shows-milky-way-is-destined-for-head-on-collision/) implies this is what could be seen in the night's sky at that time.
[![](https://i.sstatic.net/rWv6qskZ.webp)](https://i.sstatic.net/rWv6qskZ.webp)

Since the level of detail of the arm of the Milky Way Galaxy in this image doesn't represent what the naked eye can see, I assumed there is no chance details of the structure of Andromeda would be visible as well.

**Tags:** milky-way, night-sky, naked-eye, collision, andromeda


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## 3 answers

### Answer by username_1 on 2024-11-25. Score: 12

The "surface brightness" of Andromeda will remain about the same. It will be roughly similar to the surface brightness of the Milky Way. From dark skies, the milky way is a lot more visible than you might think, but it won't be as bright as it can appear in long-exposure photographs.


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### Answer by username_2 on 2024-11-25. Score: 6

Once the Milkyway and the Andromeda Galaxy start to interact more intensely, Andromeda will become more and more like our own Milkyway. Of course one can make out some structure (like we do with light and dark dust clouds in front of or embedded in the Milkyway, with some directions offering more stars (towards our Galaxy's centre) and others less.

Overall, looking from the inside like we do, there will be more of a Milkyway (our current one extended by Andromeda), but it will basically look the same, possibly over more extended regions in the Sky as we might then have approximately two disks to look at which might be somewhat oblique to eachother with wild interactions mixing them gradually, all while we are sitting in one of the disks.

It's a wild mixing by cosmological standards - still it's a mostly collision-less interaction between the two galaxies when looking at the individual stars. The end result of a merger of spiral galaxies like both, Milkyway and Andromeda galaxy are, is considered to be an [elliptical galaxy](https://en.wikipedia.org/wiki/Elliptical_galaxy). Yet that result will take far longer than our host star, the Sun, will exist. Both [M51](https://de.wikipedia.org/wiki/Whirlpool-Galaxie) and [antenna galaxy](https://en.wikipedia.org/wiki/Antennae_Galaxies) are examples of interacting galaxies which start to merge - and it might be an outside view of what the joint Milkyway and Andromeda Galaxy start to look like during the initial stages of merging (the antenna galaxies are more equal-sized, thus probably the better example).

Depending in where you place your observer after the merge is finished, you night sky might look a bit different than now when within an elliptical Galaxy which has a more 3D extent than the more or less flat spiral Galaxy; the clearly-defined band of the Milkyway as we know now might be missing with a hemisphere or larger region of the sky having more stars than the other when looking inward; the amount of Gas might also be less after the initial star burst has passed which happened during the actual merger - thus fewer dark and bright clouds like [bok globules](https://en.wikipedia.org/wiki/Bok_globule) or [orion nebula](https://en.wikipedia.org/wiki/Orion_Nebula).

> **Comments:**
> **username_3**: An actual merger between Andromeda and the MW will eventually produce something like an elliptical galaxy, and so *won't* "basically look the same".  
> **username_2**: @PeterErwin eventually likely yes. Before that we will be in something nice as M51, the whirlpool galaxy, just more symmetrical. By then Earth is gone though :)  
> **username_3**: No, it will look more like [the Antenna Galaxies](https://en.wikipedia.org/wiki/Antennae_Galaxies). Major mergers  don’t make for grand design spirals…  
> **username_4**: @PeterErwin is right; the Milky Way is *currently* considered to have a well-defined structure, but the merger will completely obliterate it, definitely not maintain it.  
> **username_2**: Allright. My consideration as described previously ended at the stage of contact, similar to what the image in the OP's posting shows. It's right that mergers usually are considered to create elliptical galaxies - and that might change the view after it is finished; I added that in another paragraph.  

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### Answer by username_4 on 2024-11-25. Score: 4

Galaxies are not singular points of light like stars are - they are diffuse, and emit light across their entire structure.

With that being said, you're correct in believing that Andromeda's shape would appear more vague to the naked eye, with a distinguishable core and a dim ellipse-like outer region.

You would only be able to replicate the image you provided by taking a long exposure picture of the night sky, but to the unaided eye you would see nowhere near that level of detail and color, simply because you're viewing the entire galaxy's light spread out over a large area.


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