<p>At any one time, an average observer can see about 2,500 stars in a clear dark sky. Note that eyesight varies and sharp-eyed individuals may be able to see a half-magnitude dimmer stars than the average eye (<a href="https://en.wikipedia.org/wiki/Apparent_magnitude" rel="nofollow">apparent magnitude</a> is a scale in which each integer is $2.51$ ($100^{0.2}$) times brighter or dimmer than the next consecutive integer.) A very dark sky may enable magnitude $+7.5$ or even $+8$ stars to be seen, but in a typical "dark" non-urban sky the limit is often $+5.5$ to $+6.5$.</p>

<p>Supernovae can potentially be seen as far as 13 billion light-years (ly) away, essentially from the 'edge' of our observable universe. So, it's not saying much to say that a supernova might be seen across a distance of 100,000 ly.</p>

<p>Some types of supernovae can be over $-22$ in <a href="https://en.wikipedia.org/wiki/Absolute_magnitude" rel="nofollow">absolute magnitude</a> — where absolute magnitude is defined as their apparent magnitude if they were observed from a 32.6 ly distance (to be honest, I'm not sure if supernovae absolute brightness is defined in exactly this same way). By way of comparison, the Sun's abs. mag. is $+4.8$ (lower numbers indicate brighter stars).</p>

<p>Because of the dust and interstellar medium, the possible distance we can see is just a small fraction of the size of the Milky Way. In reality, few stars are bright enough to be seen over 400 ly away. Deneb which has an estimated distance of 2,600 ly (but may be as close as 1,550 ly, the large uncertainty is due to its variation in brightness). Only 6 visible stars are thought to be farther from us than 1,000 ly.</p>

<p>So, to sum up, looking inwards into the Milky Way, our visibility is very restricted to the nearest 1,000–2,000 ly (while the MW disk's radius is 50,000 to 90,000 ly and we're about 27,000 ly on this side of center, but only the brightest stars are visible from more than about 400 ly away.</p>

<p>While looking away, we can see the Andromeda Galaxy (but not its individual stars) which is 2,500,000 ly from us. In other words, most people blame dust for the poor visibility, but that's mostly only relevant for telescopes. For us, our limited eye-sight is the real barrier (not to mention the dearth of really dark skies).</p>

CC BY-SA 3.0
2016-08-21T20:50:13.993Z
Some of the facts are incorrect. The median naked eye stars is at a distance of 400 light years. About 10% of naked eye stars are further than 1000 light years. See http://physics.stackexchange.com/questions/164720/the-fainter-the-star-the-further-away-it-is/164745#164745 Supernovae cannot be "seen" at distances of 13 billion light years. Most supernovae in our Galaxy could not be "seen".
ProfRob
CC BY-SA 3.0
2016-06-04T20:39:44.567Z
2016-06-04T22:08:04.913Z
2016-06-04T22:08:04.913Z
Li Zhi
<p>An average eye can see about 4000 objects in the night sky.  The brightest are planets from the Solar system, and almost all others are stars from our galaxy, the Milky Way. Some other galaxies may be spotted, but very few.</p>

<p>Even accounting for just half the sky, that is a very very tiny proportion of our galaxy, estimated to contain between 100 and 400 billion stars, around .000003%!  The galaxy itself being an average one among more than 100 billion galaxies in the observable universe...</p>

CC BY-SA 3.0
2015-03-25T02:00:57.703Z
When we see that small percentage, are those all stars local to our area? We don't see a general smear of stars from the core of the galaxy, for example?
joseph.hainline
CC BY-SA 3.0
2015-03-25T02:10:20.880Z
Most stars are probably close by, but we see the giants and super-giants across the galaxy, and of course the super-novae.  From time to time, a super-nova from another galaxy can be seen with the naked-eye, as happened in 1885 (Andromeda), and more recently in 1940 (NGC 253), 1972 (NGC 5253), 1993 (M81) and 2004 (NGC 2403).
chqrlie
CC BY-SA 3.0
2015-03-25T02:42:53.767Z
@joseph.hainline We can't see the core of the galaxy because there is a dust cloud blocking the view.
LDC3
CC BY-SA 3.0
2015-03-25T09:49:14.637Z
The 4000 stars that you mention here are mostly very close to the Sun - median distance about  They are not what makes up the "Milky Way" referred to in the question. So although you are right that we see a small fraction of the stars, your argument is is quantitatively incorrect by orders of magnitude.
ProfRob
CC BY-SA 3.0
2015-03-25T12:01:02.330Z
Secondly, the question is not asking what fraction of stars can be seen, but rather refers to the distance extent to which we can see. This is defined by the most luminous stars as you say in a comment above and so it doesn't matter what fraction of stars are seen so long as they trace the bulk population. But we do not see *individual* stars to great distances either - only a few thousand light years with the naked eye.
ProfRob
CC BY-SA 3.0
2015-03-25T12:02:49.637Z
Sorry, missed a critical number out - the median distance of naked eye resolved stars is about 400 light years.
ProfRob
CC BY-SA 3.0
2015-03-25T22:51:02.937Z
@Rob Jeffries: your remarks are welcome. I should have been more concise: we are not seeing the bulk of the galaxy, but merely a vague fraction of the local arm.  Regarding how much of the Milky Way is visible to the naked eye, almost nothing: less than 2 in 100,000 stars and none of the darker matter.
chqrlie
CC BY-SA 3.0
2015-03-25T23:01:07.613Z
I suppose what I mean is your eye probes a much bigger distance actually. Dust basically cuts the Milky Way off at about 2kpc (well beyond where you see individual stars), so you can "see" about  6% of the MW interior to the Sun's orbit.
ProfRob
CC BY-SA 3.0
2015-03-25T23:08:31.010Z
That's a bigger fraction than I anticipated.  The question then becomes: what is the shape of what we don't see with respect to what we see of the MW?
chqrlie
CC BY-SA 3.0
2015-03-25T01:59:39.750Z
2015-03-25T02:02:04.977Z
2015-03-25T02:02:04.977Z
chqrlie
<p>I'm not sure exactly how to answer this, but certainly most of what you see is local.   In the southern hemisphere we see the "milky Way" as a kind of lighter smudge across the sky:  <a href="http://s.ngm.com/2010/12/milky-way/img/milky-way-galaxy-615.jpg" rel="nofollow">http://s.ngm.com/2010/12/milky-way/img/milky-way-galaxy-615.jpg</a>, but that's probably still only a small fraction of the Milky-way, probably mostly the closest arm.    The farthest star we can see easily from the eye (some people might be able to see further ones), but that's Deneb, about 1,550 light years away, about 2% the distance of the other side of the Milky Way.</p>

<p><a href="http://www.armaghplanet.com/blog/how-far-away-is-the-farthest-star.html" rel="nofollow">http://www.armaghplanet.com/blog/how-far-away-is-the-farthest-star.html</a></p>

<p>If you know where to look, you can see Andromeda, but that's cause it's a mostly unobstructed view.   <a href="http://www.public.asu.edu/~rjansen/localgroup/NVWS99B_03.gif" rel="nofollow">http://www.public.asu.edu/~rjansen/localgroup/NVWS99B_03.gif</a></p>

<p>We could likely see a milky way super-nova much more distant than Deneb and the Milky Way should have about 1 supernova every 50-100 years or so.   The last milky-way supernova that was seen was the Kepler supernova in 1604, about 21,000 light years away and at the time it was brighter than all the other stars in the sky briefly.  <a href="http://phys.org/news/2012-09-kepler-supernovae.html" rel="nofollow">http://phys.org/news/2012-09-kepler-supernovae.html</a></p>

<p>but however you calculate it, we only see a small percentage of the Milky Way.</p>

CC BY-SA 3.0
2015-03-25T05:35:56.643Z
2015-03-25T05:35:56.643Z
userLTK
<p>When we see the Milky Way on a dark night are we seeing the bulk of the galaxy, or just our local arm? How much of the milky way is visible to the naked eye on a dark night?</p>

CC BY-SA 3.0
2015-03-25T02:21:42.810Z
Similar to this question: http://astronomy.stackexchange.com/questions/6005/arent-there-more-naked-eye-visible-stars-in-the-milky-way-plane?rq=1 - maybe considered close enough to be a duplicate?
joseph.hainline
<galaxy><milky-way><naked-eye>
How much of the Milky Way is visible to the naked eye from earth?
joseph.hainline
# How much of the Milky Way is visible to the naked eye from earth?

(Asked by: username_0 on 2015-03-25)

When we see the Milky Way on a dark night are we seeing the bulk of the galaxy, or just our local arm? How much of the milky way is visible to the naked eye on a dark night?

**Tags:** galaxy, milky-way, naked-eye
> **Comments:**
> **username_0**: Similar to this question: http://astronomy.stackexchange.com/questions/6005/arent-there-more-naked-eye-visible-stars-in-the-milky-way-plane?rq=1 - maybe considered close enough to be a duplicate?  

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## 3 answers

### Answer by username_1 on 2016-06-04. Score: 3 | Accepted answer

At any one time, an average observer can see about 2,500 stars in a clear dark sky. Note that eyesight varies and sharp-eyed individuals may be able to see a half-magnitude dimmer stars than the average eye ([apparent magnitude](https://en.wikipedia.org/wiki/Apparent_magnitude) is a scale in which each integer is $2.51$ ($100^{0.2}$) times brighter or dimmer than the next consecutive integer.) A very dark sky may enable magnitude $+7.5$ or even $+8$ stars to be seen, but in a typical "dark" non-urban sky the limit is often $+5.5$ to $+6.5$.

Supernovae can potentially be seen as far as 13 billion light-years (ly) away, essentially from the 'edge' of our observable universe. So, it's not saying much to say that a supernova might be seen across a distance of 100,000 ly.

Some types of supernovae can be over $-22$ in [absolute magnitude](https://en.wikipedia.org/wiki/Absolute_magnitude) — where absolute magnitude is defined as their apparent magnitude if they were observed from a 32.6 ly distance (to be honest, I'm not sure if supernovae absolute brightness is defined in exactly this same way). By way of comparison, the Sun's abs. mag. is $+4.8$ (lower numbers indicate brighter stars).

Because of the dust and interstellar medium, the possible distance we can see is just a small fraction of the size of the Milky Way. In reality, few stars are bright enough to be seen over 400 ly away. Deneb which has an estimated distance of 2,600 ly (but may be as close as 1,550 ly, the large uncertainty is due to its variation in brightness). Only 6 visible stars are thought to be farther from us than 1,000 ly.

So, to sum up, looking inwards into the Milky Way, our visibility is very restricted to the nearest 1,000–2,000 ly (while the MW disk's radius is 50,000 to 90,000 ly and we're about 27,000 ly on this side of center, but only the brightest stars are visible from more than about 400 ly away.

While looking away, we can see the Andromeda Galaxy (but not its individual stars) which is 2,500,000 ly from us. In other words, most people blame dust for the poor visibility, but that's mostly only relevant for telescopes. For us, our limited eye-sight is the real barrier (not to mention the dearth of really dark skies).

> **Comments:**
> **username_2**: Some of the facts are incorrect. The median naked eye stars is at a distance of 400 light years. About 10% of naked eye stars are further than 1000 light years. See http://physics.stackexchange.com/questions/164720/the-fainter-the-star-the-further-away-it-is/164745#164745 Supernovae cannot be "seen" at distances of 13 billion light years. Most supernovae in our Galaxy could not be "seen".  

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### Answer by username_3 on 2015-03-25. Score: 2

An average eye can see about 4000 objects in the night sky. The brightest are planets from the Solar system, and almost all others are stars from our galaxy, the Milky Way. Some other galaxies may be spotted, but very few.

Even accounting for just half the sky, that is a very very tiny proportion of our galaxy, estimated to contain between 100 and 400 billion stars, around .000003%! The galaxy itself being an average one among more than 100 billion galaxies in the observable universe...

> **Comments:**
> **username_0**: When we see that small percentage, are those all stars local to our area? We don't see a general smear of stars from the core of the galaxy, for example?  
> **username_3**: Most stars are probably close by, but we see the giants and super-giants across the galaxy, and of course the super-novae.  From time to time, a super-nova from another galaxy can be seen with the naked-eye, as happened in 1885 (Andromeda), and more recently in 1940 (NGC 253), 1972 (NGC 5253), 1993 (M81) and 2004 (NGC 2403).  
> **username_4**: @joseph.hainline We can't see the core of the galaxy because there is a dust cloud blocking the view.  
> **username_2**: The 4000 stars that you mention here are mostly very close to the Sun - median distance about  They are not what makes up the "Milky Way" referred to in the question. So although you are right that we see a small fraction of the stars, your argument is is quantitatively incorrect by orders of magnitude.  
> **username_2**: Secondly, the question is not asking what fraction of stars can be seen, but rather refers to the distance extent to which we can see. This is defined by the most luminous stars as you say in a comment above and so it doesn't matter what fraction of stars are seen so long as they trace the bulk population. But we do not see *individual* stars to great distances either - only a few thousand light years with the naked eye.  
> **username_2**: Sorry, missed a critical number out - the median distance of naked eye resolved stars is about 400 light years.  
> **username_3**: @Rob Jeffries: your remarks are welcome. I should have been more concise: we are not seeing the bulk of the galaxy, but merely a vague fraction of the local arm.  Regarding how much of the Milky Way is visible to the naked eye, almost nothing: less than 2 in 100,000 stars and none of the darker matter.  
> **username_2**: I suppose what I mean is your eye probes a much bigger distance actually. Dust basically cuts the Milky Way off at about 2kpc (well beyond where you see individual stars), so you can "see" about  6% of the MW interior to the Sun's orbit.  
> **username_3**: That's a bigger fraction than I anticipated.  The question then becomes: what is the shape of what we don't see with respect to what we see of the MW?  

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### Answer by username_5 on 2015-03-25. Score: 1

I'm not sure exactly how to answer this, but certainly most of what you see is local. In the southern hemisphere we see the "milky Way" as a kind of lighter smudge across the sky: <http://s.ngm.com/2010/12/milky-way/img/milky-way-galaxy-615.jpg>, but that's probably still only a small fraction of the Milky-way, probably mostly the closest arm. The farthest star we can see easily from the eye (some people might be able to see further ones), but that's Deneb, about 1,550 light years away, about 2% the distance of the other side of the Milky Way.

<http://www.armaghplanet.com/blog/how-far-away-is-the-farthest-star.html>

If you know where to look, you can see Andromeda, but that's cause it's a mostly unobstructed view. <http://www.public.asu.edu/~rjansen/localgroup/NVWS99B_03.gif>

We could likely see a milky way super-nova much more distant than Deneb and the Milky Way should have about 1 supernova every 50-100 years or so. The last milky-way supernova that was seen was the Kepler supernova in 1604, about 21,000 light years away and at the time it was brighter than all the other stars in the sky briefly. <http://phys.org/news/2012-09-kepler-supernovae.html>

but however you calculate it, we only see a small percentage of the Milky Way.


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