<p>In early times of galaxy formation you would have seen a sky similar to this <a href="https://esahubble.org/images/heic1214a/" rel="nofollow noreferrer">Hubble Extreme Deep Field image</a>. A sky filled with small, irregularly shaped, young galaxies and galaxy predecessor fragments (sub-galaxies). <a href="https://www.e-education.psu.edu/astro801/content/l9_p7.html" rel="nofollow noreferrer">Galaxies probably formed bottom-up from smaller fragments</a>.</p>
<p>Further back in time it would have been dark. Hydrogen clouds would begin to contract, as predecessors of first stars (<a href="http://www2.astro.psu.edu/users/rbc/a534/redman.pdf" rel="nofollow noreferrer">population III</a>) and <a href="http://jwst.nasa.gov/firstlight.html" rel="nofollow noreferrer">clusters of stars</a>.</p>
<p>Even further in the past (redshift between 300 and 400) the sky would have been glowing red by what we now call <a href="http://en.wikipedia.org/wiki/Cosmic_microwave_background" rel="nofollow noreferrer">cosmic microwave background</a>.</p>

CC BY-SA 4.0
2014-02-21T15:07:53.290Z
2022-04-03T18:35:21.103Z
2022-04-03T18:35:21.103Z
Gerald
<p>As @Gerald stated in his excellent answer, the Hubble XDF photo might describe the night sky - many irregular, blue galaxies. As the redshift at 12.9 billion light years is about <span class="math-container">$z=6.5$</span>, the universe was 7.5 times smaller in radius at the time compared to what it is now.</p>
<p>To answer @RogerWood's questions:</p>
<blockquote>
<p>More detailed description of the appearance of the night sky in 12.9 billion years BCE -including star-types, magnitudes, colors, apparent motion, distribution, etc. - with some solid explanation.</p>
</blockquote>
<p>This rendition of a young Milky Way from Wikipedia might give a realistic impression as to how the night sky may have looked in the early universe.
<a href="https://upload.wikimedia.org/wikipedia/commons/2/28/A_firestorm_of_star_birth_%28artist%E2%80%99s_illustration%29.jpg" rel="nofollow noreferrer"><img src="https://upload.wikimedia.org/wikipedia/commons/2/28/A_firestorm_of_star_birth_%28artist%E2%80%99s_illustration%29.jpg" alt="enter image description here" /></a>
As seen, there is much more star formation hence more red (H-II regions) and blue areas (open clusters and nebulae), the central bulge of our galaxy is not as well-formed, perhaps because of a less-massive SMBH.</p>
<p>As you would expect in the young universe, most stars would be bluer, early type stars with very low metallicity (maybe population III stars?). Late-type stars that formed at that time would now be the old Population II stars we see today in galactic cores and old globular clusters. Given this distribution, the color of the night sky still would be black, but with more blue and red from hot, luminous stars and the red from star-forming regions and warm hydrogen clouds.</p>
<p>Apparent motion would essentially make no difference in the change of the night sky as everything still would be pretty far away (of the order of a few hundred to a few thousand light years) but still closer than the star-forming regions of today.</p>
<p>I hope this addresses some more detail than before, if you have any comments or concerns, let me know.</p>

CC BY-SA 4.0
2022-04-08T17:56:23.143Z
Maybe I’m mistaken, but with a current *R* value of 1, wouldn’t the *R* value at a red shift of 6.5 be .129 or roughly 7.75 times smaller since $R=1/(1+z)$?
Justin T
CC BY-SA 4.0
2022-04-08T20:45:53.797Z
@justin I admit, this is a topic I really don't understand.  It seems like they're saying the light has stretched by a factor of 7.5.  But how does that reconcile with the statement about 7% the age of the universe. Is the expansion non-linear with time?
Roger Wood
CC BY-SA 4.0
2022-04-08T20:54:32.310Z
@fasterthanlight Thanks for the answer.  Can I assume that inter-stellar spacing might be quite similar?  But In the current universe, galaxies are fairly distinct with large spaces between them (10x their diameter?). I assume this was not at all true 12.9 billion years BCE? Were both the galaxies and their spacings both a lot smaller. Maybe there would be an autocorrelation function that would look similar but have a much smaller characteristic length?
Roger Wood
CC BY-SA 4.0
2022-04-08T21:12:09.583Z
@RogerWood Yes, expansion isn't linear in time. Its rate decelerates at early times due to the mutual attraction of matter, and accelerates at later times due to dark energy. A lookback time of 12.9 Gyr corresponds to a redshift of z = 6.2, meaning that the scale factor was a = 1/(1+z) ≈ 0.14 at that time, i.e. a factor 7.2 smaller. This is true for cosmological distances; inside galaxies, where the interstellar medium is dominated by local physical conditions, it's more complicated. The gas was hotter then, and galaxies hadn't condensed as much, so the ISM wasn't necessarily any denser.
pela
CC BY-SA 4.0
2022-04-08T22:36:12.577Z
@JustinT whoops, wrong formula!
WarpPrime
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2022-04-08T22:52:21.707Z
@fasterthanlight I read that the vast majority of stars live much longer than 13 billion years, so there must have been far fewer stars back then - unless the initial rate of star formation was extremely high - which seems quite likely.
Roger Wood
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2022-04-09T00:13:17.367Z
@RogerWood In the early universe there was more gas and less metals, so larger stars were more common - you are correct that star formation was high.
WarpPrime
CC BY-SA 4.0
2022-04-09T02:00:59.627Z
@fasterthanlight Would I be right in saying probably no milky way in the sky?  I assume spiral galaxies would be rare and that the texture of the universe would be more spongy with strings and walls and blobs rather than discrete galaxies?
Roger Wood
CC BY-SA 4.0
2022-04-09T14:58:45.063Z
@RogerWood Yes, galaxy-galaxy encounters were much more common then, so building up a rotating disk is impeded at high z. There are however recent observations indicating ordered motion already at z ~ 6, though it’s probably not the norm.
pela
CC BY-SA 4.0
2022-04-08T15:51:32.603Z
2022-04-08T22:36:46.863Z
2022-04-08T22:36:46.863Z
WarpPrime
<p>If I stood on a theoretical earth at the time that galaxies were just starting to form, what would the sky have looked like?</p>
<p>Due to the smaller size of the universe would it have been densely packed with objects? If yes, what might I have seen?</p>
<p>[Edit added by Roger Wood]</p>
<p>What would the night sky have looked like in 12,900,000,000 years BCE?</p>
<p>Prompted by Hubble's discovery of <a href="https://www.nasa.gov/feature/goddard/2022/record-broken-hubble-spots-farthest-star-ever-seen/" rel="nofollow noreferrer">Earendel</a>, what would the night sky have looked like back 12.9 billion years ago? (ignoring details like the Earth and humans not existing back then),</p>
<p>Apparently this star existed at 7% the age of the universe. Does this also mean the universe was 14 times smaller and 14<sup>3</sup>=2700 times more dense than today? And the night sky would have been 14<sup>2</sup>=200 times brighter? So nearby Galaxies would be much bigger and brighter with an apparent size of several degrees in the sky. Or would distinct, well-formed galaxies even be apparent at that time? What structures would be seen? What would the population of stars be like - lots of big blue ones or a bunch of little red ones? They'd obviously all be very young.</p>

CC BY-SA 4.0
2022-04-08T17:32:19.313Z
From which viewpoint - obviously the Sun and Earth didn't exist? From within our galaxy or from intergalactic space?
ProfRob
CC BY-SA 4.0
2022-04-08T20:37:12.847Z
@ProfRob Good point. It's unclear whether our galaxy even existed. I think some discussion of the distribution of stars at that time is part of the question.  If galaxies were 2700 times more densely packed, they'd be pretty much all smushed together.
Roger Wood
<star><galaxy><hubble-telescope><night-sky><early-universe>
What would the night sky have looked like 12.9 billion years ago when galaxies first started to form?
Duke Dougal
# What would the night sky have looked like 12.9 billion years ago when galaxies first started to form?

(Asked by: username_0 on 2014-02-21)

If I stood on a theoretical earth at the time that galaxies were just starting to form, what would the sky have looked like?

Due to the smaller size of the universe would it have been densely packed with objects? If yes, what might I have seen?

[Edit added by Roger Wood]

What would the night sky have looked like in 12,900,000,000 years BCE?

Prompted by Hubble's discovery of [Earendel](https://www.nasa.gov/feature/goddard/2022/record-broken-hubble-spots-farthest-star-ever-seen/), what would the night sky have looked like back 12.9 billion years ago? (ignoring details like the Earth and humans not existing back then),

Apparently this star existed at 7% the age of the universe. Does this also mean the universe was 14 times smaller and 143=2700 times more dense than today? And the night sky would have been 142=200 times brighter? So nearby Galaxies would be much bigger and brighter with an apparent size of several degrees in the sky. Or would distinct, well-formed galaxies even be apparent at that time? What structures would be seen? What would the population of stars be like - lots of big blue ones or a bunch of little red ones? They'd obviously all be very young.

**Tags:** star, galaxy, hubble-telescope, night-sky, early-universe
> **Comments:**
> **username_1**: From which viewpoint - obviously the Sun and Earth didn't exist? From within our galaxy or from intergalactic space?  
> **username_2**: @ProfRob Good point. It's unclear whether our galaxy even existed. I think some discussion of the distribution of stars at that time is part of the question.  If galaxies were 2700 times more densely packed, they'd be pretty much all smushed together.  

---

## 2 answers

### Answer by username_3 on 2014-02-21. Score: 7

In early times of galaxy formation you would have seen a sky similar to this [Hubble Extreme Deep Field image](https://esahubble.org/images/heic1214a/). A sky filled with small, irregularly shaped, young galaxies and galaxy predecessor fragments (sub-galaxies). [Galaxies probably formed bottom-up from smaller fragments](https://www.e-education.psu.edu/astro801/content/l9_p7.html).

Further back in time it would have been dark. Hydrogen clouds would begin to contract, as predecessors of first stars ([population III](http://www2.astro.psu.edu/users/rbc/a534/redman.pdf)) and [clusters of stars](http://jwst.nasa.gov/firstlight.html).

Even further in the past (redshift between 300 and 400) the sky would have been glowing red by what we now call [cosmic microwave background](http://en.wikipedia.org/wiki/Cosmic_microwave_background).


---

### Answer by username_4 on 2022-04-08. Score: 6

As @Gerald stated in his excellent answer, the Hubble XDF photo might describe the night sky - many irregular, blue galaxies. As the redshift at 12.9 billion light years is about $z=6.5$, the universe was 7.5 times smaller in radius at the time compared to what it is now.

To answer @RogerWood's questions:

> More detailed description of the appearance of the night sky in 12.9 billion years BCE -including star-types, magnitudes, colors, apparent motion, distribution, etc. - with some solid explanation.

This rendition of a young Milky Way from Wikipedia might give a realistic impression as to how the night sky may have looked in the early universe.
[![enter image description here](https://upload.wikimedia.org/wikipedia/commons/2/28/A_firestorm_of_star_birth_%28artist%E2%80%99s_illustration%29.jpg)](https://upload.wikimedia.org/wikipedia/commons/2/28/A_firestorm_of_star_birth_%28artist%E2%80%99s_illustration%29.jpg)
As seen, there is much more star formation hence more red (H-II regions) and blue areas (open clusters and nebulae), the central bulge of our galaxy is not as well-formed, perhaps because of a less-massive SMBH.

As you would expect in the young universe, most stars would be bluer, early type stars with very low metallicity (maybe population III stars?). Late-type stars that formed at that time would now be the old Population II stars we see today in galactic cores and old globular clusters. Given this distribution, the color of the night sky still would be black, but with more blue and red from hot, luminous stars and the red from star-forming regions and warm hydrogen clouds.

Apparent motion would essentially make no difference in the change of the night sky as everything still would be pretty far away (of the order of a few hundred to a few thousand light years) but still closer than the star-forming regions of today.

I hope this addresses some more detail than before, if you have any comments or concerns, let me know.

> **Comments:**
> **username_5**: Maybe I’m mistaken, but with a current *R* value of 1, wouldn’t the *R* value at a red shift of 6.5 be .129 or roughly 7.75 times smaller since $R=1/(1+z)$?  
> **username_2**: @justin I admit, this is a topic I really don't understand.  It seems like they're saying the light has stretched by a factor of 7.5.  But how does that reconcile with the statement about 7% the age of the universe. Is the expansion non-linear with time?  
> **username_2**: @fasterthanlight Thanks for the answer.  Can I assume that inter-stellar spacing might be quite similar?  But In the current universe, galaxies are fairly distinct with large spaces between them (10x their diameter?). I assume this was not at all true 12.9 billion years BCE? Were both the galaxies and their spacings both a lot smaller. Maybe there would be an autocorrelation function that would look similar but have a much smaller characteristic length?  
> **username_6**: @RogerWood Yes, expansion isn't linear in time. Its rate decelerates at early times due to the mutual attraction of matter, and accelerates at later times due to dark energy. A lookback time of 12.9 Gyr corresponds to a redshift of z = 6.2, meaning that the scale factor was a = 1/(1+z) ≈ 0.14 at that time, i.e. a factor 7.2 smaller. This is true for cosmological distances; inside galaxies, where the interstellar medium is dominated by local physical conditions, it's more complicated. The gas was hotter then, and galaxies hadn't condensed as much, so the ISM wasn't necessarily any denser.  
> **username_4**: @JustinT whoops, wrong formula!  
> **username_2**: @fasterthanlight I read that the vast majority of stars live much longer than 13 billion years, so there must have been far fewer stars back then - unless the initial rate of star formation was extremely high - which seems quite likely.  
> **username_4**: @RogerWood In the early universe there was more gas and less metals, so larger stars were more common - you are correct that star formation was high.  
> **username_2**: @fasterthanlight Would I be right in saying probably no milky way in the sky?  I assume spiral galaxies would be rare and that the texture of the universe would be more spongy with strings and walls and blobs rather than discrete galaxies?  
> **username_6**: @RogerWood Yes, galaxy-galaxy encounters were much more common then, so building up a rotating disk is impeded at high z. There are however recent observations indicating ordered motion already at z ~ 6, though it’s probably not the norm.  

---

