<p>This is really more of a biology question, I think, so: The Mark-I Eyeball is far less sensitive to color than to intensity.  There are rods and cones in the retina. The neural signals from the rods are used to report intensity only. There are different spectral sensitivity curves for different cones (typically three types in humans), so the relative outputs from all cones are used to generate color information.  However, cones are less sensitive than rods, so for dim light such as that reaching us from nebulas, only the rods produce a neural output. </p>

CC BY-SA 3.0
2017-05-29T04:31:52.603Z
This is also why, when you look at stars with the naked eye, they're all basically white, even though in reality their color varies widely.
probably_someone
CC BY-SA 3.0
2017-05-26T11:56:48.047Z
2017-05-26T11:56:48.047Z
Carl Witthoft
<p>Looking at <a href="https://astronomy.stackexchange.com/questions/1350/are-nebulae-only-visible-from-a-distance/1354">answers to this question</a>, people seem pretty convinced that human naked eye should be able to see the colour of ionised gas/dust cloud when they are inside an emission nebula.</p>

<p>And we know <em>Solar system</em> is surrounded by <a href="https://en.wikipedia.org/wiki/Interplanetary_dust_cloud" rel="nofollow noreferrer"><em>Interplanetary dust cloud</em></a>, and possibly inside an <a href="https://en.wikipedia.org/wiki/Local_Interstellar_Cloud" rel="nofollow noreferrer"><em>Interstellar cloud</em></a>. <strong>Why don't we see a colorised space backdrop?</strong></p>

<p>Does it have to do with density of gas cloud? or how ionised they are? Does camera with long exposure see some background colour our naked eye can't?</p>

<p><em>(Excuse me for any wrong terminology.)</em></p>

CC BY-SA 3.0
2017-05-26T11:53:50.377Z
"Colorised" does not mean what you think it means.
Carl Witthoft
CC BY-SA 3.0
2017-05-26T14:46:07.463Z
@Carl-Witthoft : A link to the [dictionary](https://www.merriam-webster.com/dictionary/colorize) may help to OP.  However I confess to not knowing what the appropriate phrase might be in this case - any English experts care to enlighten me. :-)
StephenG - Help Ukraine
CC BY-SA 3.0
2017-05-26T16:06:28.977Z
@StephenG  I'd suggest  "perceived in color"
Carl Witthoft
<space><nebula><naked-eye>
Why isn't our local interstellar space colorised?
bitinn
# Why isn't our local interstellar space colorised?

(Asked by: username_0 on 2017-05-26)

Looking at [answers to this question](https://astronomy.stackexchange.com/questions/1350/are-nebulae-only-visible-from-a-distance/1354), people seem pretty convinced that human naked eye should be able to see the colour of ionised gas/dust cloud when they are inside an emission nebula.

And we know *Solar system* is surrounded by [*Interplanetary dust cloud*](https://en.wikipedia.org/wiki/Interplanetary_dust_cloud), and possibly inside an [*Interstellar cloud*](https://en.wikipedia.org/wiki/Local_Interstellar_Cloud). **Why don't we see a colorised space backdrop?**

Does it have to do with density of gas cloud? or how ionised they are? Does camera with long exposure see some background colour our naked eye can't?

*(Excuse me for any wrong terminology.)*

**Tags:** space, nebula, naked-eye
> **Comments:**
> **username_1**: "Colorised" does not mean what you think it means.  
> **username_2**: @Carl-Witthoft : A link to the [dictionary](https://www.merriam-webster.com/dictionary/colorize) may help to OP.  However I confess to not knowing what the appropriate phrase might be in this case - any English experts care to enlighten me. :-)  
> **username_1**: @StephenG  I'd suggest  "perceived in color"  

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## 1 answers

### Answer by username_1 on 2017-05-26. Score: 2

This is really more of a biology question, I think, so: The Mark-I Eyeball is far less sensitive to color than to intensity. There are rods and cones in the retina. The neural signals from the rods are used to report intensity only. There are different spectral sensitivity curves for different cones (typically three types in humans), so the relative outputs from all cones are used to generate color information. However, cones are less sensitive than rods, so for dim light such as that reaching us from nebulas, only the rods produce a neural output.

> **Comments:**
> **username_3**: This is also why, when you look at stars with the naked eye, they're all basically white, even though in reality their color varies widely.  

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