<p>The Earth image in your question is heavily edited.  The night lights are much too bright; they can only be seen with highly sensitive sensors from low earth orbit; it's not possible with current instruments to see night lights while viewing the full Earth disc (a corresponding channel was considered for the next generation American geostationary satellites, but not selected and therefore not planned).  Therefore, the night lights part is certainly a precomputed image (probably <a href="https://en.wikipedia.org/wiki/The_Blue_Marble#Black_Marble_2012" rel="noreferrer">Black Marble</a>) used to fill up the black part, like done for <a href="https://rammb.cira.colostate.edu/training/visit/quick_guides/QuickGuide_CIRA_Geocolor_20171019.pdf" rel="noreferrer">CIRAs GeoColor composite</a>.  The sunlit part of your included image also looks like it has undergone heavy post-processing beyond the usual Rayleigh correction stuff.</p>
<p>To address your question: the terminator <em>does</em> look redder from space compared to fully sunlit areas, but because it's so much darker than the fully sunlit part of the image, it's not clear.  In the image below, you can subtly see it in the clouds off the African coast that are just in the night side of the terminator.  The sun has set on ground level, but is still shining higher up.  Those clouds look redder than the ones that are still in full daylight.</p>
<p><a href="https://i.sstatic.net/f5RtsY6t.jpg" rel="noreferrer"><img src="https://i.sstatic.net/f5RtsY6t.jpg" alt="True color image" /></a></p>
<p>2023-09-26, 16:30, created using the Satpy <code>true_color_raw</code> composite, which excludes Rayleigh correction.</p>

CC BY-SA 4.0
2024-05-02T19:42:35.130Z
most photographs from space have traces of correction, this is a topic for a separate big conversation. As for this particular picture, it is a prize-winner of a space photography competition, if my memory serves me.
Vladimir Orlov
CC BY-SA 4.0
2024-05-02T19:54:47.360Z
@VladimirOrlov Certainly, they are usually corrected, but at some point it stops being a correction and starts being compositing or enhancing.  A correction is IMO based on something physical; Rayleigh correction uses a model to remove excess blue, a solar zenith correction corrects for variations in incoming solar radiation so that places near sunset look as bright as places near the sub solar point.  Enhancing is rather to make the image more appealing for the human eye, even if it's also called "gamma correction" I think that's a misnomer as it isn't correcting anything.
gerrit
CC BY-SA 4.0
2024-05-03T12:21:19.717Z
@gerrit Gamma correction _was_ a correction - fixing a translation between linear light values and non-linear CRT inputs. Gamma correction then serves to "undo" the original translation to tweak it to the particular display you are using (both because different CRTs had different curves, and because other kinds of displays worked completely differently). Of course, nowadays, "gamma correction" is not really gamma correction at all, and just became a silly way to make visuals darker or brighter (there's much better ways to do that... because that's not what gamma correction is for, duh).
Luaan
CC BY-SA 4.0
2024-05-03T12:33:10.610Z
@Luaan Thank you very much for the historical information (I learned something) and where is the image processing stack exchange to ask you about better ways to do what we're doing with gamma correction? :)  Histogram equalisation?  Log contrast adjustment?  Others?
gerrit
CC BY-SA 4.0
2024-05-03T12:46:28.123Z
@gerrit Yeah, part of the reason why "gamma correction" is still used is that it works well enough, is widely supported, and people already understand that it kind of means making the image darker or lighter :D The alternatives are many, and you need to choose - simply linearly increasing brightness usually gives worse results than abusing "gamma correction", though part of that is how used we became to wrong gamma due to poor configuration etc. I'm mostly concerned with the original gamma correction mechanism because it's important for reproducing old games :D
Luaan
CC BY-SA 4.0
2024-05-05T11:33:00.540Z
Regarding the color of the snowy areas, I think there's an additional factor that reduces visibility of their orange coloration: the blue light from the air column above them, which is brighter than the extincted orange scattered by the snow. Orange clouds are more visible (e.g. [1](https://eol.jsc.nasa.gov/SearchPhotos/photo.pl?mission=ISS063&roll=E&frame=110775), [2](https://eol.jsc.nasa.gov/DatabaseImages/ESC/large/ISS063/ISS063-E-110843.JPG)) because of being above part of the glowing atmosphere, but (continued...)
Ruslan
CC BY-SA 4.0
2024-05-05T11:33:10.170Z
(...continuation) they need special lighting: from below the mathematical horizon, so that sunlight passes through a thick layer of atmosphere horizontally to redden before being scattered by the clouds.
Ruslan
CC BY-SA 4.0
2024-05-02T14:14:07.487Z
2024-05-03T08:10:55.657Z
2024-05-03T08:10:55.657Z
gerrit
<h3>It depends how you look at it - <em>literally!</em></h3>
<p>I think there is merit to including what ProfRob wrote in his (currently deleted) answer. Sunsets are red when you look towards the sun because thicker  air scatters more of the blue light <em>sideways</em>.</p>
<p>While the ground might look a bit redder when seen from space, that blue light is also scattered upwards, so it can easily be that the <em>total</em> light seen looking down at the terminator is not significantly reddened or blued.</p>
<p>If you instead look at the terminator in the direction <em>roughly toward</em> the sun (i.e. &quot;downstream&quot;) like the Moon does during a penumbral eclipse, then the terminator will definitely look really red!</p>
<p>That's why penumbral lunar eclipses show that progressively organge, &quot;burn't umber' deep red color.</p>

CC BY-SA 4.0
2024-05-03T00:40:45.280Z
2024-05-03T00:40:45.280Z
uhoh
<p>As you know, the sun's rays at dawn and sunset are painted in golden-pink colors, and the objects on which they fall, primarily clouds, snow covers and water surfaces, are also colored. This happens because the red part of the spectrum is better refracted by the earth's atmosphere.
It would be completely logical to expect that earth's terminator line in photographs from space would be colored in the same color.
And look something like this:
<a href="https://i.sstatic.net/jtoiEKPF.jpg" rel="noreferrer"><img src="https://i.sstatic.net/jtoiEKPF.jpg" alt="enter image description here" /></a></p>
<p>But look really like this:</p>
<p><a href="https://i.sstatic.net/7AScVHue.jpg" rel="noreferrer"><img src="https://i.sstatic.net/7AScVHue.jpg" alt="enter image description here" /></a></p>
<p>Source: nasa.gov</p>

CC BY-SA 4.0
2024-05-02T12:39:01.760Z
That you can see the night side lights at all when the daylight side isn't overexposed makes me think the Earth image you have chosen to include is a composite of some kind, rather than a single photograph.
notovny
CC BY-SA 4.0
2024-05-02T13:09:55.293Z
You can see Earth's "red" atmosphere during a lunar eclipse from the surface if the Moon due to refraction, if it helps.
4NT4R3S
CC BY-SA 4.0
2024-05-02T19:27:46.107Z
To exemplify the answer below, consider the 360 degree sunset you see during a total solar eclipse.  That redness is always there, it's just you can only see it once the sun and it's local effects are blocked out.  Example image: https://i.pinimg.com/736x/7f/71/b5/7f71b50fd8793e1edc5b51b23494b70d.jpg
Greg Miller
CC BY-SA 4.0
2024-05-03T00:52:55.323Z
I'm not qualified to answer, but Rayleigh scattering goes both ways though an atmosphere.   Would that contribute toward or subtract away from the effect OP is looking for ?
Criggie
CC BY-SA 4.0
2024-05-03T11:23:23.250Z
Why would you expect this effect in a photograph taken from _outside_ the atmosphere?  The colors come from atmospheric diffraction so why would you expect to see them when the light hitting the camera hasn't gone through the atmosphere? Am I missing something obvious here?
terdon
CC BY-SA 4.0
2024-05-03T12:59:23.203Z
@terdon  In satellite images, red objects remain red.
I don't think that clouds and snow that look red from below will appear white from above.
Vladimir Orlov
CC BY-SA 4.0
2024-05-03T13:05:19.043Z
Red objects are red because they reflect light in the red spectrum, that's different. As you point out in your question, sunsets are red because of light being refracted and scattered by the atmosphere, a completely different process. Since you are taking the photograph from outside the atmosphere, light is not scattered and shouldn't be red. Right?
terdon
CC BY-SA 4.0
2024-05-04T03:55:33.280Z
@terdon It was though. The light went from the sun, *through the atmosphere*, *was scattered*, then hit the earth, then came back through the atmosphere, and hit the camera.
Mooing Duck
<earth>
Why is the terminator line not orange-red in photos from space?
Vladimir Orlov
# Why is the terminator line not orange-red in photos from space?

(Asked by: username_0 on 2024-05-02)

As you know, the sun's rays at dawn and sunset are painted in golden-pink colors, and the objects on which they fall, primarily clouds, snow covers and water surfaces, are also colored. This happens because the red part of the spectrum is better refracted by the earth's atmosphere.
It would be completely logical to expect that earth's terminator line in photographs from space would be colored in the same color.
And look something like this:
[![enter image description here](https://i.sstatic.net/jtoiEKPF.jpg)](https://i.sstatic.net/jtoiEKPF.jpg)

But look really like this:

[![enter image description here](https://i.sstatic.net/7AScVHue.jpg)](https://i.sstatic.net/7AScVHue.jpg)

Source: nasa.gov

**Tags:** earth

> **Comments:**
> **username_1**: That you can see the night side lights at all when the daylight side isn't overexposed makes me think the Earth image you have chosen to include is a composite of some kind, rather than a single photograph.  
> **username_2**: You can see Earth's "red" atmosphere during a lunar eclipse from the surface if the Moon due to refraction, if it helps.  
> **username_3**: To exemplify the answer below, consider the 360 degree sunset you see during a total solar eclipse.  That redness is always there, it's just you can only see it once the sun and it's local effects are blocked out.  Example image: https://i.pinimg.com/736x/7f/71/b5/7f71b50fd8793e1edc5b51b23494b70d.jpg  
> **username_4**: I'm not qualified to answer, but Rayleigh scattering goes both ways though an atmosphere.   Would that contribute toward or subtract away from the effect OP is looking for ?  
> **username_5**: Why would you expect this effect in a photograph taken from _outside_ the atmosphere?  The colors come from atmospheric diffraction so why would you expect to see them when the light hitting the camera hasn't gone through the atmosphere? Am I missing something obvious here?  
> **username_0**: @username_5  In satellite images, red objects remain red. I don't think that clouds and snow that look red from below will appear white from above.  
> **username_5**: Red objects are red because they reflect light in the red spectrum, that's different. As you point out in your question, sunsets are red because of light being refracted and scattered by the atmosphere, a completely different process. Since you are taking the photograph from outside the atmosphere, light is not scattered and shouldn't be red. Right?  
> **username_6**: @username_5 It was though. The light went from the sun, *through the atmosphere*, *was scattered*, then hit the earth, then came back through the atmosphere, and hit the camera.  

---

## 2 answers

### Answer by username_7 on 2024-05-02. Score: 19

The Earth image in your question is heavily edited. The night lights are much too bright; they can only be seen with highly sensitive sensors from low earth orbit; it's not possible with current instruments to see night lights while viewing the full Earth disc (a corresponding channel was considered for the next generation American geostationary satellites, but not selected and therefore not planned). Therefore, the night lights part is certainly a precomputed image (probably [Black Marble](https://en.wikipedia.org/wiki/The_Blue_Marble#Black_Marble_2012)) used to fill up the black part, like done for [CIRAs GeoColor composite](https://rammb.cira.colostate.edu/training/visit/quick_guides/QuickGuide_CIRA_Geocolor_20171019.pdf). The sunlit part of your included image also looks like it has undergone heavy post-processing beyond the usual Rayleigh correction stuff.

To address your question: the terminator *does* look redder from space compared to fully sunlit areas, but because it's so much darker than the fully sunlit part of the image, it's not clear. In the image below, you can subtly see it in the clouds off the African coast that are just in the night side of the terminator. The sun has set on ground level, but is still shining higher up. Those clouds look redder than the ones that are still in full daylight.

[![True color image](https://i.sstatic.net/f5RtsY6t.jpg)](https://i.sstatic.net/f5RtsY6t.jpg)

2023-09-26, 16:30, created using the Satpy `true_color_raw` composite, which excludes Rayleigh correction.

> **Comments:**
> **username_0**: most photographs from space have traces of correction, this is a topic for a separate big conversation. As for this particular picture, it is a prize-winner of a space photography competition, if my memory serves me.  
> **username_7**: @username_0 Certainly, they are usually corrected, but at some point it stops being a correction and starts being compositing or enhancing.  A correction is IMO based on something physical; Rayleigh correction uses a model to remove excess blue, a solar zenith correction corrects for variations in incoming solar radiation so that places near sunset look as bright as places near the sub solar point.  Enhancing is rather to make the image more appealing for the human eye, even if it's also called "gamma correction" I think that's a misnomer as it isn't correcting anything.  
> **username_8**: @username_7 Gamma correction _was_ a correction - fixing a translation between linear light values and non-linear CRT inputs. Gamma correction then serves to "undo" the original translation to tweak it to the particular display you are using (both because different CRTs had different curves, and because other kinds of displays worked completely differently). Of course, nowadays, "gamma correction" is not really gamma correction at all, and just became a silly way to make visuals darker or brighter (there's much better ways to do that... because that's not what gamma correction is for, duh).  
> **username_7**: @username_8 Thank you very much for the historical information (I learned something) and where is the image processing stack exchange to ask you about better ways to do what we're doing with gamma correction? :)  Histogram equalisation?  Log contrast adjustment?  Others?  
> **username_8**: @username_7 Yeah, part of the reason why "gamma correction" is still used is that it works well enough, is widely supported, and people already understand that it kind of means making the image darker or lighter :D The alternatives are many, and you need to choose - simply linearly increasing brightness usually gives worse results than abusing "gamma correction", though part of that is how used we became to wrong gamma due to poor configuration etc. I'm mostly concerned with the original gamma correction mechanism because it's important for reproducing old games :D  
> **username_9**: Regarding the color of the snowy areas, I think there's an additional factor that reduces visibility of their orange coloration: the blue light from the air column above them, which is brighter than the extincted orange scattered by the snow. Orange clouds are more visible (e.g. [1](https://eol.jsc.nasa.gov/SearchPhotos/photo.pl?mission=ISS063&roll=E&frame=110775), [2](https://eol.jsc.nasa.gov/DatabaseImages/ESC/large/ISS063/ISS063-E-110843.JPG)) because of being above part of the glowing atmosphere, but (continued...)  
> **username_9**: (...continuation) they need special lighting: from below the mathematical horizon, so that sunlight passes through a thick layer of atmosphere horizontally to redden before being scattered by the clouds.  

---

### Answer by username_10 on 2024-05-03. Score: 10

### It depends how you look at it - *literally!*

I think there is merit to including what ProfRob wrote in his (currently deleted) answer. Sunsets are red when you look towards the sun because thicker air scatters more of the blue light *sideways*.

While the ground might look a bit redder when seen from space, that blue light is also scattered upwards, so it can easily be that the *total* light seen looking down at the terminator is not significantly reddened or blued.

If you instead look at the terminator in the direction *roughly toward* the sun (i.e. "downstream") like the Moon does during a penumbral eclipse, then the terminator will definitely look really red!

That's why penumbral lunar eclipses show that progressively organge, "burn't umber' deep red color.


---

