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Old 11-17-2009, 03:53 PM   #1
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Can we see stars that no longer exist with our naked eye?

Stars can burn for hundreds of millions to billions of years long..... the larger the mass of a star, the more brief and violent its life.

I'm fairly sure we can see, with telescopes, stars that are billions of light years away, and based on our observations we would expect them to be nearing their deaths. So, we can infer that the star we are seeing no longer exists, because we are seeing it billions of years ago.

But do all the examples of these stars require telescopes? Are there any stars that we can see in the night sky with our naked eye that no longer exist?
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Old 11-17-2009, 04:02 PM   #2
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Re: Can we see stars that no longer exist with our naked eye?

In clear nights, outside of the city, you can even see other galaxies with the naked eye, so some stars far away enough that we didnīt notice their passing yet should definitely be visible too, yes.

For example, the Andromeda Galaxy is 2.5 a million LY away and is visible in good nights.
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Old 11-17-2009, 04:16 PM   #3
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Re: Can we see stars that no longer exist with our naked eye?

yes but 2.5 million ly is a small distance given the lifespan of a star, and a galaxy is much brighter.
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Old 11-17-2009, 04:29 PM   #4
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Re: Can we see stars that no longer exist with our naked eye?

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Originally Posted by teh_mewse View Post
yes but 2.5 million ly is a small distance given the lifespan of a star, and a galaxy is much brighter.

What does the lifespan of a star really have to do with your question? Alpha Centauri is 4.2 or so light years away, it could have blown up 3 years ago and we wouldn't know it yet. Many visible stars are within 10-20 light years away, and could very welll no longer exist at this time.

The problem with your question is that there really isn't a way to know the answer. It doesn't matter how strong your telescope is, it still isn't going to see the light before it reaches earth. So there could easily be hundreds of stars that we can see with the naked eye that no longer exist. Or there could be none.

Maybe I'm just not understanding the question. That's entirely possible, also.
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Old 11-17-2009, 05:02 PM   #5
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Re: Can we see stars that no longer exist with our naked eye?

I doubt we could ever know for sure if a star we are seeing light from still exists but could probably work out a probability.

Like a star of a certain size and estimated age has <blank> percent chance of being destroyed in Y million years
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Old 11-17-2009, 05:11 PM   #6
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Re: Can we see stars that no longer exist with our naked eye?

I think heīs pondering the possibility of a single star in the nightsky that is visible to the naked eye having died by now, without us knowing.

With about 5000 stars being visible in a good night, and the most distant stars we can make out without telescopes maybe 10,000 lightyears away, this possibility is quite small, i think.

Also, with modern instruments, changes in the light of a star would certainly be noticeable such a small timespan as 10,000 years before its death. Beteigeuze, the bright red star in the Orion, is thought to go supernova in the next 1,500 - 150,000 years. It is thought it will be very big and bright as the moon on our
nightsky when this happens, and fullfill the night on our planet with red light.
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Old 11-17-2009, 05:18 PM   #7
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Re: Can we see stars that no longer exist with our naked eye?

The answer is simply 'yes'
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Old 11-17-2009, 06:12 PM   #8
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Re: Can we see stars that no longer exist with our naked eye?

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The answer is simply 'yes'
As a tiny part of a distant galaxy, yes, thatīs what i was trying to say in my first post. As single stars on the nightsky, its highly unlikely. So iīd say its not so simple.

If the average lifespan of a star is 5,000,000,000 years, the average distance of visible stars is, i dont know, 1000 lightyears, and there are 5000 visible stars on the sky, the chance that one of them is dead yet is only 1 : 1000.

Maybe its a little higher than that, as the galaxy is old and stars are aging, making it more likely that some have died by now. But i doubt this factor is immensly important.
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Old 11-17-2009, 06:43 PM   #9
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Re: Can we see stars that no longer exist with our naked eye?

The question wasn't about likelihood.
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Old 11-17-2009, 06:49 PM   #10
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Re: Can we see stars that no longer exist with our naked eye?

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The question wasn't about likelihood.
I am referring to this question by OP:

"Are there any stars that we can see in the night sky with our naked eye that no longer exist?"

Are you honestly saying "yes" is a better answer than "We canīt know for sure, but it is not likely", or are you referring to a different question?
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Old 11-17-2009, 07:02 PM   #11
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Re: Can we see stars that no longer exist with our naked eye?

You're the one answering a different question.

The correct answer is easily "yes" it's possible to see a star that is already dead.

How likely it is that any given star that we're seeing w/ the naked eye is in fact already dead is an entirely different question.
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Old 11-17-2009, 07:15 PM   #12
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Re: Can we see stars that no longer exist with our naked eye?

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Originally Posted by durkadurka33 View Post
You're the one answering a different question.

The correct answer is easily "yes" it's possible to see a star that is already dead.
You misunderstand what OP has wanted to ask, I even *quoted* his question *word for word* in my last post.

I think you have only read the thread title and got drawn to a wrong conclusion about what OP wanted to know.

fwiw, I too got confused a bit b/c of the title at first, but its actually quite clear what OP wants to know.
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Old 11-17-2009, 08:21 PM   #13
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Re: Can we see stars that no longer exist with our naked eye?

Yes if a star in the sky has died we can still see it for a while depending on the stars distance, the further away the longer time it takes before it 'dissapears'. The further away the star the more likely the star is already dead. This goes for all stars.

Am pretty sure the star is in a completely different location also due to everything wizzing round space and expanding.
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Old 11-17-2009, 08:41 PM   #14
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Re: Can we see stars that no longer exist with our naked eye?

Quote:
Originally Posted by CommanderCorm View Post
I am referring to this question by OP:

"Are there any stars that we can see in the night sky with our naked eye that no longer exist?" [verbatim quote]
Quote:
Originally Posted by durkadurka33 View Post
You're the one answering a different question.

The correct answer is easily "yes" it's possible to see a star that is already dead.
Answering the wrong question:
[ ] CommanderCorm
[X] durkadurka33
[X] others ITT

I have nothing else to add, CmdrCorn said it all.
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Old 11-17-2009, 09:03 PM   #15
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Re: Can we see stars that no longer exist with our naked eye?

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Originally Posted by teh_mewse View Post
Stars can burn for hundreds of millions to billions of years long..... the larger the mass of a star, the more brief and violent its life.

I'm fairly sure we can see, with telescopes, stars that are billions of light years away, and based on our observations we would expect them to be nearing their deaths. So, we can infer that the star we are seeing no longer exists, because we are seeing it billions of years ago.

But do all the examples of these stars require telescopes? Are there any stars that we can see in the night sky with our naked eye that no longer exist?
I see that there's people saying that people are answering the 'wrong' question, but I'll take a shot (at least it's interesting information, if I'm answering the 'wrong' question).

Betelguese: from the Wikipedia article: It is possible that Betelgeuse will become a supernova,[4][29] which will be the brightest ever recorded, outshining the Moon in the night sky.[29] Considering its size and age of 8.5 million years, old for its size class, it may explode within the next thousand years.[29] Since its rotational axis is not toward the Earth and also because of its 640 light year distance,[29] Betelgeuse's supernova will not cause a gamma ray burst in the direction of Earth large enough to damage its ecosystems.

If it will explode sometime within the next 1000 years, and 640 light years distance, there's about a 2/3 chance we are seeing light from Betelguese, but it no longer exists. Given the size of the galaxy, I think this is the best one can do (give a % chance that the star no longer exists, rather than *know* it doesn't)
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