From the “I’ve been alive for 32 years and I’m afraid to ask” File:
I am nearsighted, ridiculously nearsighted, and even WITH my contacts, I sometimes can’t see street signs or billboards hundreds of yards away. So why is it, that tiny pinpoint like lights, BILLIONS OF MILES AWAY can be seen with my contacts. I…can barely explain my question correctly, but trust me, it keeps me up at night.
Any thoughts?
Whoops. GQ. I was going to post a humorous response, but instead, I’ll just say long time no see, jarbabyj.
and no, that wasn’t the humorous response.
Well, stars aren’t exactly tiny pinpoints of light. They are gigantic balls of flaming gas thousands of times bigger than our planet. Like the sun, they are millions of miles away but also ridiculously gigantic, so their brightness makes up for their distance.
Being nearsighted won’t necessarily affect whether you can see something far away but how well you can resolve its details. It will affect the number of stars you can see, though. I’m also nearsighted and need to put on my glasses to see more stars. Most stars look rather like blurry smudges instead of pretty little points of light to my unaided eyes.
Tiny pinpoints of light? There are no such things. There are dime and quarter sized points of light. Is that what you are talking about?
No, really, I read about this. The distance is irrelevant. The contrast is important, and that’s what you see. Nobody can see detail, so we all see the stars pretty much the same.
I going to go now and let somebody who knows what they’re talking about explain. But I’m kinda right. 
The difference in luminosity between the star and the street light is pretty huge. For lack of a better metaphor, it’s like the glow of a cigarette two blocks away versus the glow of a nuclear detonation many miles away.
hmmm, I guess I’m sort of understanding, but if someone drew a white dot on piece of black paper and held it 200 yards away, even with my best contacts, I couldn’t see it, but I could see stars, even the tiny ones in the plieades (or however that’s spelled).
First of all, eyesight is the ability to resolve patterns, or resolve two dots as separate dots. It doesn’t take much eyesight to know that there is a point of light. (Although if your eyesight is bad enough, the star’s light gets blurred over such a large area that it can’t be seen.) Also, optically speaking, 100 yards away is almost indistinguishable from infinity. Take a manual focus camera and focus it to an object 100 yards away - the lens will be almost at the infinity mark. Trying to see a star 100 light-years away isn’t much harder than seeing a light bulb 100 yards away.
As for why stars are bright enough for us to see - well, the only possible answer is that “they’re really bright!” They are suns, remember.
A really obvious point that I think nonetheless needs making: the majority of us to live in light-polluted areas only see the very brightest stars, which are far far brighter than our sun.
What you don’t seem to realize is how few stars you actually see.
When the telescope points to the area “between” visible stars: There are more points of light between any two visible ones than the total of visible ones in the whole sky.
And when our telescopes are better, that ratio will rise further.
True, but then a white dot on a black piece of paper doesn’t produce its own light. Replace “a white dot on piece of black paper” with “a lit candle at night”, and you’d probably have no trouble seeing it at all.
I was going to suggest poking a hole in the paper and putting a bright light behind it. Same effect, though.
Photons go for miles and miles before they fall down and go out.
Well, they go an indefinite amount of distance before something absorbs them or deflects them away from their former path, and though the human eye is capable of responding to a single photon it’s usually not in a state of perfect receptivity due to other, brighter sources of light.
(Of course, you could nitpick that nitpick even further by pointing out that photons aren’t really real at all. ;))
What do stars look like to you? Do you see them as sharp points or sort of fuzzy circles? I’m guessing you see them as mostly slightly fuzzy blobs, in which case there’s no mystery at all. After all, the light is hitting your eye, and your problem is focus, not sensitivity. If you see them as sharply resolved pinpoints, then I’d have to think about this a bit more.
[QUOTE=Yumblie]
Well, stars aren’t exactly tiny pinpoints of light. They are gigantic balls of flaming gas thousands of times bigger than our planet. Like the sun, they are millions of miles away but also ridiculously gigantic, so their brightness makes up for their distance.
You are correct on every point, except the “flaming gas” part. There is no fire or flames involved. If this were the case, most stars would have burned out long ago. Hydrogen atoms being fused into Helium atoms under gravitational pressure by the billions of tons per second gives off photons of light as merely a byproduct.
[QUOTE=TLC1]
Well, it sort of depends on your definition of “flaming gas”. Ever see a picture of a
solar prominence? I’m pretty sure that hydrogen and helium plasma superheated to the point that it radiates in the ultraviolet spectrum would qualify as “flaming”. Granted, it’s not undergoing oxidation as we know it, but that’s probably because even if there were oxidizing materials around, the temperatures are so high that the chemical bonds would be ripped apart.
A good example of a common light source that can be seen from a good distance, even in daylight, is a welders arc. The actual arc is quite small.
Yes, I am also nearsighted like crazy- and i can see stars just fine. However, here’s the rub- even when looking through a fairly good telescope- planets all show up a fuzzy discs of various colors.
Stars were never discs or even “fuzzy blobs”- they were just points of light with a “starring effect” around them.
You should wear your glasses when looking through a telescope.
You know that, huh?
Distinguish between brightness and resolution, jarbabyj.
You have good enough eyesight that you can see a bright flashlight, a lantern, or a bright torch at night a mile away – but you may not be able to make out which one of them it is – just that somewhere over there somebody is carrying a light source.
What you’re saying is that you cannot resolve street signs, billboards, etc., at a distance – you cannot make them out clearly enough to perceive their contents. Clearly you can see them – unless your absence from the boards resulted from your having an accident because you crashed into a billboard you couldn’t see! It’s just that you cannot resolve them – cannot make out clearly their contents.
Many invertebrates have “eyes” that don’t resolve, just sense light sources and things moving and therefore changing what light is reflected off them into their simple eyes. In other words, a fly cannot see a fly-swatter as the object you and I would look at – just something moving towards them that it would be advisable to avoid.
No star can be resolved – perceived as a sphere of incandescent gas – not only by the naked eye but even by the most powerful telescopes. Interferometry, where images from separate, distant telescopes at the same moment are digitally interfaced to produce the effect of a telescope with an effective diameter of the distance between the telescopes, can resolve several of the nearer giant stars – there are a couple of photographs of Betelgeuse produced by this technique.
But anybody who is not totally blind, including many legally blind people, can see the light sources that are stars – at least the brighter stars.
Wow. This is one of those questions that I didn’t even know I wanted to know the answer to until I learn the answer.
(Someday I’ll have to ask why with my nearsightedness I can take off my glasses and see a car but can’t tell what color it is.)