Bare with me on this as clearly there is something fundamentally wrong with my understand of light particles, distance and stars but should it not be case that sometimes you should not be able to see them.
Since light travels in a straight line (mostly), and their distance are massive and my eye is so very small the tiniest of angles from which the particle leaves the star would become ernomous variations by the time it reached me.
With that in mind, even with the insane number of particles being released, shouldn’t they become so wildly diffuse and spread out that they become to faint to detect or diffuse enough that I see the star then move 2 feet away and don’t.
I guess an anology would be that a torch works fine on a wall 10 feet away but won’t light up a spot a 100 feet away even though all the particles are travelling in a straight line.
If I can see a star from every single position on my side of the planet how isn’t that lighting up the whole sky or are a few particles enough to make my retina work and see a very small point of light.
Thanks
In: Physics
You’re already correct.
>my eye is so very small the tiniest of angles from which the particle leaves the star would become ernomous variations by the time it reached me. With that in mind, even with the insane number of particles being released…
Yep, that’s how **insane** the number of photons being released is. Even that far away, a pupil-sized target is always getting hit by at least a few.
>or are a few particles enough to make my retina work and see a very small point of light.
Yes that’s it, the other factor is just how sensitive your retina is. A single-digit number of photons entering the eye is enough to be registered and perceived.
What you are talking about is called [the Inverse Square Law](https://en.wikipedia.org/wiki/Inverse-square_law) in physics, and if you read the article, it comes down to yes, light “spreads out” but also the number of photons emitted by a star is something ridiculous like 10^45 per second, so even if you divide by the square of the distance (in kilometers not light-years), you still have 10^x photons reaching the tiny surface that is your eye lens, enough to see the stars.
That said, astronomers estimate that we only see about 4000 light years around, and that is a very small part of the galaxy, which is 100,000 light years in diameter. Basically [about this much](https://qph.cf2.quoracdn.net/main-qimg-08c5a0a88beae0b31f4fc99f68eb8887).
So yeah, the Inverse Square Law effect does spread out the photons to the point where we don’t see stars anymore, past 4,000 light years or so. Telescopes have much bigger lenses, sensors that are much more sensitive than the eye, and also collect photons over long periods of time (long exposure).
You only see the light that is directly entering your eye (it won’t necessarily have travelled the whole way in a straight line but that’s another matter). The torch is not analogous at all because you are positioned at the source of the light and receiving the light reflected from the wall not, as in the case of the star, billions of miles away and receiving the light directly. If you were standing on the star then you would indeed see its light spreading out at least in so far as it reflects back from the various objects that orbit it.
The stars you see produce enough light constantly to register on your retina. There are millions of stars that you don’t see because they do not whether due to relative dimness at source, extreme distances, intervening objects, or light “pollution” on Earth.
The eye is not a camera, it doesn’t work like a camera.
To “light up the sky” starlight (or moonlight for that matter) has to interact with the parts of the atmosphere that aren’t between your eye and the light source. When that happens, with clouds on a moonlit night for example, you might see moonlight diffusely from the cloud but people standing in the “shadow” of that cloud don’t see the moon as a result. [sample](https://news.yale.edu/sites/default/files/styles/featured_media/public/ynews-238597223.jpg?itok=incx5bBX&c=a75e254fe1da31f2732f6b0d7bce1413 )
The torch analogy isn’t completely wrong, the light intensity varies as 1 over the square of the distance. But, stars are insanely bright, and the ones we can see are even brighter than the Sun.
Each of those tiny pinpricks of light are from a star as large or many times larger than our Sun, a few photons from each star is enough for you just to make out the close bright stars, some stars in our Milky Way are invisible to the human eye as they are a combination of too far away or not bright enough.
I mean you’re basically right with everything you said. I think you just need to accept how insane it is that light/stars work that way.
>Since light travels in a straight line (mostly), and their distance are massive and my eye is so very small the tiniest of angles from which the particle leaves the star would become ernomous variations by the time it reached me.
This shows just how many photons are emitted from stars. It’s an unfathomable amount. It’s so much that, yes, it can travel across the galaxy, hit your eye, and you can perceive it. Because stars radiate light in all directions, technically the light from a star is hitting every part of Earth’s surface that is directly exposed to it. It’s faint enough to not illuminate Earth, but strong enough for you to perceive it. Unlike the sun, which is so close that it’s power lights up our planet and makes it impossible for our eyes to look right at it. Stars are just versions of our sun much farther away.
>With that in mind, even with the insane number of particles being released, shouldn’t they become so wildly diffuse and spread out that they become to faint to detect
Yes, and they do. The stars you see in the sky are only the stars that are relatively close to us. Every single star you see is just the stars within our own galaxy. You are not seeing a single star from another galaxy because, as you said, the light has been diffused so much over the immense distances between galaxies. The only thing you can see outside our galaxy with your bare eye is the Andromeda galaxy. On a clear night with no light pollution, you can see a slight blur about the size of your thumb, and that’s the entire Andromeda galaxy, the next closest galaxy to us. In short, the stars you see are close enough for their light to reach us and yet be powerful enough for us to see, and everything else is so far away that their light is not perceivable by our naked eye.
>I guess an anology would be that a torch works fine on a wall 10 feet away but won’t light up a spot a 100 feet away even though all the particles are travelling in a straight line.
This is exactly the same as what I just described about stars outside of our galaxy. But stars are infinitely more powerful than a torch, so you need to amplify the scale to hundreds of thousands of lightyears.
>If I can see a star from every single position on my side of the planet how isn’t that lighting up the whole sky or are a few particles enough to make my retina work and see a very small point of light.
Yes, exactly right.
The distance of the star is only offset by how insanely large, hot, and energy dense a star is. The light waves being emitted are so dense that even light years away, they are still clustered enough to see.
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