How can I see stars.

Question

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

Answer 1

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).