<p>Some of the light will also get absorbed in the path. Even though there is no light in the desert, light coming from other distant cities ( even countries) will make more impact as the star is near the horizon compared to stars that are visible clearly. Its not like the air pollution is dense in Horizon, Horizon is just an illusion.</p>

CC BY-SA 4.0
2021-08-15T11:12:44.533Z
@uhoh Ha ! Thats some of the vital information to be added in the answer ! :)
Kavin Ishwaran
CC BY-SA 4.0
2021-08-15T11:14:40.463Z
https://en.wikipedia.org/wiki/Air_mass_(astronomy)#Calculation
uhoh
CC BY-SA 4.0
2021-08-15T12:03:01.790Z
"this is the scenario only if there is no light in the path-plane of the light coming from the star" -- what does that mean?
Peter Erwin
CC BY-SA 4.0
2021-08-15T12:04:02.470Z
Extinction due to absorption and scattering of light along the path through the atmosphere is *always* a factor.
Peter Erwin
CC BY-SA 4.0
2021-08-15T12:21:22.007Z
@PeterErwin I forgot to Edit that, I added that for a different factor (refraction), but as its impact is too small I removed it, but I forgot to delete some sentences associated with it and its one of them
Kavin Ishwaran
CC BY-SA 4.0
2021-08-15T10:59:19.690Z
2021-08-15T12:22:06.380Z
2021-08-15T12:22:06.380Z
Kavin Ishwaran
<p>I believe the correct answer is perspective. It's the same reason the full moon can sometimes look gigantic when it is just rising above the horizon, but the same moon looks the size of a dime up in the middle of the vast night sky.</p>
<p>I think what happens is, by comparison to the whole universe that we can see when standing on Earth, a section of that space would have to &quot;scrunch down&quot; to maintain the correct view from earth. Something like this:</p>
<p><a href="https://i.sstatic.net/4Ky8u.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/4Ky8u.jpg" alt="demonstrating the effect of perspective and why our horizon appears astralphobic" /></a></p>
<p>(blowing up the 1/36th chunk of starry sky also blew up the sizes of the stars so I just hit the really visible stars with a 1x1px and substituted in a black background to demonstrate the effect).</p>

CC BY-SA 4.0
2021-08-16T18:33:27.140Z
I don't think this is correct. I couldn't really follow your argument, but the Moon doesn't change apparent size when close to the horizon. The angular diameter of the Moon is always about 0.5°. Maybe I don't understand what you are saying
Prallax
CC BY-SA 4.0
2021-08-16T18:38:17.863Z
The moon doesn't change apparent size when close to the horizon? In Missouri it does.
CWill
CC BY-SA 4.0
2021-08-16T18:49:40.337Z
Ahahah ;)  Next time you see the moon, try to compare it with a finger when having the arm extended in front of your eyes. You should be able to see that its size doesn't change. Also, check this out https://solarsystem.nasa.gov/news/1191/the-moon-illusion-why-does-the-moon-look-so-big-sometimes/
Prallax
CC BY-SA 4.0
2021-08-16T20:08:50.987Z
The same is true for the sun...but the article lacks a real explanation, which is disappointing.  Perhaps it's as simple as our eyes being more dilated as an object near the horizon is less bright.
rtaft
CC BY-SA 4.0
2021-08-17T08:21:12.310Z
@CWill no it doesn’t. How would it?
Tim
CC BY-SA 4.0
2021-08-17T11:21:37.333Z
The correct answer has already been given by James K, and I'm afraid your "explanation" doesn't make any sense.
Peter Erwin
CC BY-SA 4.0
2021-08-17T22:12:48.500Z
"by comparison to the whole universe that we can see when standing on Earth" – um, the *whole universe*? With the naked eye we can only see the nearest and/or brightest stars of our own galaxy, plus the Andromeda Galaxy, the two Magellanic Clouds and the Triangulum Galaxy. That's an infinitesimal fraction of the observable universe.
Chappo Hasn't Forgotten
CC BY-SA 4.0
2021-08-17T23:50:56.240Z
@ChappoHasn'tForgottenMonica ok, inartfully said, but what I meant was "the whole part of the universe we can see." The vast expanse of visible sky.
CWill
CC BY-SA 4.0
2021-08-17T23:55:32.263Z
@Tim This is starting to weird me out a little. Has no one here ever noticed how the moon just coming over the horizon can APPEAR to be much larger than it APPEARS when it is up in the middle of the sky on a cloudless night?
CWill
CC BY-SA 4.0
2021-08-17T23:58:01.670Z
@PeterErwin After I wrote my answer, I read the other answers, and agree mine is not the correct answer. lesson learned. However, I believe my answer would also have SOME impact, albeit, negligible.
CWill
CC BY-SA 4.0
2021-08-18T07:47:05.823Z
@CWill millions of people https://en.wikipedia.org/wiki/Moon_illusion
Tim
CC BY-SA 4.0
2021-08-16T18:20:22.697Z
2021-08-16T18:26:29.213Z
2021-08-16T18:26:29.213Z
CWill
<p>When you look towards the horizon you are looking through a much greater thickness of air.   The air does absorb some light.  Dense air near surface absorbs more, and if you look towards the horizon you are looking thought a great distance of dense air.</p>
<p>It is not &quot;pollution&quot; per se, though atmospheric aerosols and smoke can exacerbate the effect. Water vapour also absorbs light, and of course any haze  or mist will absorb more.</p>
<p>If there are wildfires, dust or air pollution, the &quot;extinction&quot; of stars will be greater. Smoke can travel very long distances (I've known smoke from wildfires in Spain to have a very noticeable effect in the UK). In deserts, there can be windblown dust that has a similar effect. However, even with pristine air, the extinction of stars near the horizon will still occur.</p>

CC BY-SA 4.0
2021-08-15T10:59:31.063Z
There are fires all over parts of the US and Europe, perhaps a big part of it COULD BE pollution *per se*? e.g. [Western wildfire smoke is contributing to New York City's worst air quality in 15 years](https://edition.cnn.com/2021/07/21/weather/us-western-wildfires-wednesday/index.html)
uhoh
CC BY-SA 4.0
2021-08-15T16:01:00.037Z
@uhoh Pollution could exacerbate it, but the phenomenon will be apparent even in pristine air.
Ryan_L
CC BY-SA 4.0
2021-08-15T23:08:24.547Z
@Ryan_L I said the same thing [here](https://astronomy.stackexchange.com/questions/45305/why-are-fewer-stars-seen-next-to-the-horizon/45306?noredirect=1#comment98993_45305). Pollution from large wildfires could certainly *dominate the OP's experience* during this fire season in the northern hemisphere if that's where they are, and should not simply be dismissed out of hand in an answer. Answers should strive to be more than just statements that are not necessarily incorrect about a topic.
uhoh
CC BY-SA 4.0
2021-08-16T08:54:53.017Z
@Voile I don't see how that's relevant. Absorption due to both natural and anthropogenic particles (e.g. wildfires, volcanos, pollution) can be a huge factor. Comments of the form "Nobody cares" don't have any effect on this fact.
uhoh
CC BY-SA 4.0
2021-08-16T09:20:23.693Z
Just returning to the question,  I have already mentioned "pollution" (in the form of aerosols and smoke) But please look again at the original question.  The misconception is twofold:  "Extinction of stars is only due to light pollution.",  and "Extinction of stars is due to air pollution".  Now light and air pollution do cause stars to be less visible, but the crux of my answer is that extinction will occur even without it.  It is not pollution *of itself* that causes this, but the longer sight line through dense air near the horizon.  In the desert, a particular issue is windblown dust.
James K
CC BY-SA 4.0
2021-08-16T09:30:23.033Z
Note that the atmosphere doesn't need to absorb any light to obscure the stars; scattering works too (example: thin cirrus).  I suspect scattering is still dominant over absorption in pristine air, but I haven't done the maths.
gerrit
CC BY-SA 4.0
2021-08-16T12:31:55.903Z
And of course light pollution tends to be greatest closer to the ground, thus when you're looking at a smaller angle to the horizon.
jwenting
CC BY-SA 4.0
2021-08-16T14:40:03.527Z
@gerrit yes, something like "attenuation of direct light" might be better.
uhoh
CC BY-SA 4.0
2021-08-16T17:20:15.570Z
For some numbers, there's about 100km of air between the ground and space when looking straight up (0-degrees from zenith).  When looking to the horizon at 70-degrees there is about three times as much air and by 80-degrees from zenith you're looking through about [six times as much air mass](https://epistulaeastronomicae.wordpress.com/2019/01/09/observing-through-the-earths-atmosphere-light-path-vs-zenith-angle/) compared to looking straight up.  That's a huge difference.
J...
CC BY-SA 4.0
2021-08-15T10:21:06.770Z
2021-08-16T09:23:52.893Z
2021-08-16T09:23:52.893Z
James K
<p>I was in the desert the other day, in an area that was free of light pollution.</p>
<p>While it was easy to see the stars above us, I noticed that near the horizon, even when there is no distance light, we can see almost no stars.</p>
<p>Is this normal? What is causing this? Is it air pollution that covers the Earth and is denser when looking at the horizon? Is it just the density of the atmosphere itself?</p>

CC BY-SA 4.0
2021-08-15T11:03:10.273Z
Are you in any part of the world that could have atmospheric contamination from fires? e.g. [Western wildfire smoke is contributing to New York City's worst air quality in 15 years](https://edition.cnn.com/2021/07/21/weather/us-western-wildfires-wednesday/index.html)
uhoh
CC BY-SA 4.0
2021-08-15T11:07:20.110Z
@uhoh No, no fire/smoke contamination.
riorio
CC BY-SA 4.0
2021-08-15T11:13:09.797Z
The effect can reach thousands of kilometers. I understand if you don't want to mention a location, but it really may factor in strongly. The effect happens even for clear air, it just becomes more dramatic when the air has particulates. Volcanic eruptions can fill the entire planet's atmosphere with attenuating particles, the Earth even cools measurably.
uhoh
CC BY-SA 4.0
2021-08-15T12:08:55.120Z
As James K points out in his answer, this is a generic and universal effect of the Earth's atmosphere; the basic physics of it was worked on in the 18th Century. Things like light pollution and other forms of pollution can make it worse, but it's always there.
Peter Erwin
CC BY-SA 4.0
2021-08-15T12:09:59.073Z
More simply: you've probably noticed that the Sun is fainter when it's very close to or on the horizon. Same phenomenon.
Peter Erwin
<amateur-observing><atmospheric-effects><light-pollution>
Why are fewer stars seen next to the horizon?
riorio
# Why are fewer stars seen next to the horizon?

(Asked by: username_0 on 2021-08-15)

I was in the desert the other day, in an area that was free of light pollution.

While it was easy to see the stars above us, I noticed that near the horizon, even when there is no distance light, we can see almost no stars.

Is this normal? What is causing this? Is it air pollution that covers the Earth and is denser when looking at the horizon? Is it just the density of the atmosphere itself?

**Tags:** amateur-observing, atmospheric-effects, light-pollution

> **Comments:**
> **username_1**: Are you in any part of the world that could have atmospheric contamination from fires? e.g. [Western wildfire smoke is contributing to New York City's worst air quality in 15 years](https://edition.cnn.com/2021/07/21/weather/us-western-wildfires-wednesday/index.html)  
> **username_0**: @username_1 No, no fire/smoke contamination.  
> **username_1**: The effect can reach thousands of kilometers. I understand if you don't want to mention a location, but it really may factor in strongly. The effect happens even for clear air, it just becomes more dramatic when the air has particulates. Volcanic eruptions can fill the entire planet's atmosphere with attenuating particles, the Earth even cools measurably.  
> **username_2**: As username_9 points out in his answer, this is a generic and universal effect of the Earth's atmosphere; the basic physics of it was worked on in the 18th Century. Things like light pollution and other forms of pollution can make it worse, but it's always there.  
> **username_2**: More simply: you've probably noticed that the Sun is fainter when it's very close to or on the horizon. Same phenomenon.  

---

## 3 answers

### Answer by username_9 on 2021-08-15. Score: 35 | Accepted answer

When you look towards the horizon you are looking through a much greater thickness of air. The air does absorb some light. Dense air near surface absorbs more, and if you look towards the horizon you are looking thought a great distance of dense air.

It is not "pollution" per se, though atmospheric aerosols and smoke can exacerbate the effect. Water vapour also absorbs light, and of course any haze or mist will absorb more.

If there are wildfires, dust or air pollution, the "extinction" of stars will be greater. Smoke can travel very long distances (I've known smoke from wildfires in Spain to have a very noticeable effect in the UK). In deserts, there can be windblown dust that has a similar effect. However, even with pristine air, the extinction of stars near the horizon will still occur.

> **Comments:**
> **username_1**: There are fires all over parts of the US and Europe, perhaps a big part of it COULD BE pollution *per se*? e.g. [Western wildfire smoke is contributing to New York City's worst air quality in 15 years](https://edition.cnn.com/2021/07/21/weather/us-western-wildfires-wednesday/index.html)  
> **username_10**: @username_1 Pollution could exacerbate it, but the phenomenon will be apparent even in pristine air.  
> **username_1**: @username_10 I said the same thing [here](https://astronomy.stackexchange.com/questions/45305/why-are-fewer-stars-seen-next-to-the-horizon/45306?noredirect=1#comment98993_45305). Pollution from large wildfires could certainly *dominate the OP's experience* during this fire season in the northern hemisphere if that's where they are, and should not simply be dismissed out of hand in an answer. Answers should strive to be more than just statements that are not necessarily incorrect about a topic.  
> **username_1**: @Voile I don't see how that's relevant. Absorption due to both natural and anthropogenic particles (e.g. wildfires, volcanos, pollution) can be a huge factor. Comments of the form "Nobody cares" don't have any effect on this fact.  
> **username_9**: Just returning to the question,  I have already mentioned "pollution" (in the form of aerosols and smoke) But please look again at the original question.  The misconception is twofold:  "Extinction of stars is only due to light pollution.",  and "Extinction of stars is due to air pollution".  Now light and air pollution do cause stars to be less visible, but the crux of my answer is that extinction will occur even without it.  It is not pollution *of itself* that causes this, but the longer sight line through dense air near the horizon.  In the desert, a particular issue is windblown dust.  
> **username_11**: Note that the atmosphere doesn't need to absorb any light to obscure the stars; scattering works too (example: thin cirrus).  I suspect scattering is still dominant over absorption in pristine air, but I haven't done the maths.  
> **username_12**: And of course light pollution tends to be greatest closer to the ground, thus when you're looking at a smaller angle to the horizon.  
> **username_1**: @username_11 yes, something like "attenuation of direct light" might be better.  
> **username_13**: For some numbers, there's about 100km of air between the ground and space when looking straight up (0-degrees from zenith).  When looking to the horizon at 70-degrees there is about three times as much air and by 80-degrees from zenith you're looking through about [six times as much air mass](https://epistulaeastronomicae.wordpress.com/2019/01/09/observing-through-the-earths-atmosphere-light-path-vs-zenith-angle/) compared to looking straight up.  That's a huge difference.  

---

### Answer by username_3 on 2021-08-15. Score: 0

Some of the light will also get absorbed in the path. Even though there is no light in the desert, light coming from other distant cities ( even countries) will make more impact as the star is near the horizon compared to stars that are visible clearly. Its not like the air pollution is dense in Horizon, Horizon is just an illusion.

> **Comments:**
> **username_3**: @username_1 Ha ! Thats some of the vital information to be added in the answer ! :)  
> **username_1**: https://en.wikipedia.org/wiki/Air_mass_(astronomy)#Calculation  
> **username_2**: "this is the scenario only if there is no light in the path-plane of the light coming from the star" -- what does that mean?  
> **username_2**: Extinction due to absorption and scattering of light along the path through the atmosphere is *always* a factor.  
> **username_3**: @PeterErwin I forgot to Edit that, I added that for a different factor (refraction), but as its impact is too small I removed it, but I forgot to delete some sentences associated with it and its one of them  

---

### Answer by username_4 on 2021-08-16. Score: -8

I believe the correct answer is perspective. It's the same reason the full moon can sometimes look gigantic when it is just rising above the horizon, but the same moon looks the size of a dime up in the middle of the vast night sky.

I think what happens is, by comparison to the whole universe that we can see when standing on Earth, a section of that space would have to "scrunch down" to maintain the correct view from earth. Something like this:

[![demonstrating the effect of perspective and why our horizon appears astralphobic](https://i.sstatic.net/4Ky8u.jpg)](https://i.sstatic.net/4Ky8u.jpg)

(blowing up the 1/36th chunk of starry sky also blew up the sizes of the stars so I just hit the really visible stars with a 1x1px and substituted in a black background to demonstrate the effect).

> **Comments:**
> **username_5**: I don't think this is correct. I couldn't really follow your argument, but the Moon doesn't change apparent size when close to the horizon. The angular diameter of the Moon is always about 0.5°. Maybe I don't understand what you are saying  
> **username_4**: The moon doesn't change apparent size when close to the horizon? In Missouri it does.  
> **username_5**: Ahahah ;)  Next time you see the moon, try to compare it with a finger when having the arm extended in front of your eyes. You should be able to see that its size doesn't change. Also, check this out https://solarsystem.nasa.gov/news/1191/the-moon-illusion-why-does-the-moon-look-so-big-sometimes/  
> **username_6**: The same is true for the sun...but the article lacks a real explanation, which is disappointing.  Perhaps it's as simple as our eyes being more dilated as an object near the horizon is less bright.  
> **username_7**: @username_4 no it doesn’t. How would it?  
> **username_2**: The correct answer has already been given by username_9, and I'm afraid your "explanation" doesn't make any sense.  
> **username_8**: "by comparison to the whole universe that we can see when standing on Earth" – um, the *whole universe*? With the naked eye we can only see the nearest and/or brightest stars of our own galaxy, plus the Andromeda Galaxy, the two Magellanic Clouds and the Triangulum Galaxy. That's an infinitesimal fraction of the observable universe.  
> **username_4**: @ChappoHasn'tForgottenMonica ok, inartfully said, but what I meant was "the whole part of the universe we can see." The vast expanse of visible sky.  
> **username_4**: @username_7 This is starting to weird me out a little. Has no one here ever noticed how the moon just coming over the horizon can APPEAR to be much larger than it APPEARS when it is up in the middle of the sky on a cloudless night?  
> **username_4**: @PeterErwin After I wrote my answer, I read the other answers, and agree mine is not the correct answer. lesson learned. However, I believe my answer would also have SOME impact, albeit, negligible.  
> **username_7**: @username_4 millions of people https://en.wikipedia.org/wiki/Moon_illusion  

---

