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# How far can the human eye see?

When I look out into the night sky and I espy the Large Magellanic Cloud, which is at a distance of 152,000 light years, or 893 551 056 723 922 432 miles, am I actually looking that far or does the light only become visible from a certain distance?
Understanding that the light is constantly moving towards me, where is the Human Optical limit?
All the stars we see are located within the Milky Way.
The only objects we can observe unaided outside the Milky Way are the two Magellanic Clouds, The Andromeda Galaxy and in optimal conditions the Triangulum Galaxy M33
ArishMell · 70-79, M
It's not the distance that counts but the brightness.

As far as our sight is concerned it does not matter if the dot of light is a single star a hundred light years away or a huge galaxy a hundred thousand light-years away, if the intensity of the light when it reaches the Earth is the same. It is still a dot of light of certain intensity arriving on a retina of very small area.

What distance does affect is the perspective - the optical illusion that seems to shrink objects with distance until eventually they are too "small" to detect by the unaided eye.

If that star were to be 500 hundred light-years away, ie. 5 times as far away, the intensity of light would be 1/25 of that at 100 LY; so possibly too faint to see, but it may also be too small anyway. Even if we could we would not know by sight alone if it is a bright star a long way off or dimmer one a lot closer.

You could spot it with a telescope of 50mm aperture though, because its object-lens area is 25 times that of your 10mm aperture iris so can collect 25 times the "amount" of light. Or put another way, it catches a lot of light that would miss our eye!

It still won't tell you how far away it is. Determining astronomical distances relies on lots of extremely high-accuracy observations and formidable mathematics.

[Accuracy or precision? I can never remember the difference!]
windinhishair · 61-69, M
The light is here when you see it. It enters your eye, which is a receptor, and you "see" it. That light left the Large Magellanic Cloud 152,000 years ago. You are not seeing what it looks like now. A year from now, you are seeing the light that left 152,000 years before then, or 152,001 years before now. In essence, it can be looked at as a form of time travel, with each point of light representing a different time before the present. The light you will see next year is still one light year away right now, and in one year it will be here.
ArishMell · 70-79, M
@windinhishair It certainly shows the sheer scale and majesty of the Universe.....

Sometimes I wonder if the astronomers using the most powerful telescopes they have, compare photographs taken a year or two apart and spot "new" arrivals in the later images.
windinhishair · 61-69, M
@ArishMell They DO compare images. This is one of the ways they identify stars that have gone supernova or comets that are approaching Earth.
ArishMell · 70-79, M
@windinhishair Thankyou. I must admit I'd not thought of that.
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Gusman · 61-69, M
@phuckoffNuno My view is blocked by the Blue Mountains Range 😄
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Gumba1000 · M
I'd like to know the answer too
Gumba1000 · M
@Gusman Would eagles be able to see further still? 🤔
Gusman · 61-69, M
@Gumba1000 More perplexity to my question. 😄
JimboSaturn · 51-55, M
@Gusman When it hits your eye. You don't see light coming up to you, you perceive it when it hits your optic nerve.
BarbossasHusband · 36-40, M
Well... I gotta take my glasses off to see wether or not they're dirty, so... Not that far?
JimboSaturn · 51-55, M
It the stars are bright enough we can see incredibly far. Some people can see M81 and M82 two galaxies 12 Million light years away!
JimboSaturn · 51-55, M
@JimboSaturn And you see the object when the light coming from that object hits your retina so the light has to get all the way to you.
Gusman · 61-69, M
@JimboSaturn Which is why I ask my question.
M32 is 19 Million light years, or 111 693 882 090 490 298 368 miles away.😮
How far away is the light when we can see it?
JimboSaturn · 51-55, M
@Gusman When it hits our eyes. We can only see anything when the light hits our eyes.