If stars are hundreds of light years away, then how do we know they're still there?

Question

The star could have died before it's light reached Earth. What if all we're seeing is just an image, a light, of the star, and not the real thing? If it takes hundreds of years for light, (which moves really quickly- it's how long it takes for you to "see" something, like an apple or a computer, right?)

And when we do watch a star die, are we really watching it die hundreds of light years after it's REAL death?

Or is it all just relative to the lifespan of the star?

Answer 1

That's exactly right. In fact, the light from our own Sun is 8 minutes old, so if the Sun blinked out seven minutes ago, we won't find out for another minute! The same is true for light that bounces off of your best friend and hits your eye. If your friend had disappeared a fraction of a second before the light hit your eye, you wouldn't know it. Well, that's only a fraction of a second, but you see the point. Astronomers can judge from the age of a star--where it is in it's life span, as you suggest--what the liklihood is that it is still there. But we can't know for sure. It is a safe hypothesis that a young star that is only 100 light years away is still there because 100 years is nothing compared to the lifespan of a star.

The useful thing about looking out into space at stars that are even 10 billion years old is that it is like looking back in time. Think about that. If we look at all galaxies that are 5 billion light years away, then what we are really doing is looking at the Universe as it was 5 billion years ago!

So, rather than "really watching it die", I would say that we are really watching the Universe be born. This is the reason that astronomers get excited each time they are able to see further and further into space. They are looking back further and further in time. This helps scientists better understand our Universe.

Although the lifespan of stars is part of it, looking so far away--and so far back in time--is more closely related to the lifespan of the Universe. I always think it's cool every time I realize that we can look back in time...

Answer 2

Stars Light Years

Answer 3

Well, most stars last millions to billions of years, so the likelihood that they will die while the light is in transit is pretty low (for those only a few hundred light years away, that is). On the other hand, when we see a supernova that is, say, 160,000 light years away (there was one in 1986 at that distance), we see what happened 160,000 years ago. So, yes, the star was dead long before we saw it go.

This really isn't that unusual though. When you hear something, you here what happened when the sound started out, not at the time you hear it. So when you hear a plane in the sky, the sound appears to come from a place behind where the plane is. SImialrly, thunder is heard several seconds after the lightning flash since the sound has to travel from the lightning flash to you. The only difference with stars and light is that light is as fast as anything goes, so we don't have other things to compare to.

Answer 4

The stars we see that are that close can have lifespans of many billions of years. A couple of centuries doesn´t really matter. And even if the stars does manage to die within centuries then its remains will still be up there. Nebulae takes millenia to dissipate and white dwarfs take billions of years to cool down to invisibility. We can tell when a star is close to death as those are the red supergiants. The star Betelgeuse in Orion is roughly 425 lightyears ago and is very close to death. It might have died when Tycho Brahe, who studied supernovae, lost his nose in a duel. The light from the blast would still be on its way here and we wouldn´t know it.

Answer 5

what if, hypothetically speaking, I were looking at a star 1000 light-years a way that died 500 years ago, if I were to observe while traveling to that star on a spaceship traveling way faster then the speed of light, would it suddenly seem explode and disappear?

Answer 6

You don't know they are still there, except by inference, meaning that we know stars exist for millions to billions of years, so it is very likely that all those within hundreds of light years away are still there when their light reaches us.

Also astronomers recognise stars that are near their end, and if the star looks young or even middle-aged it is very unlikely that it will have died with a few hundred years.

Answer 7

how far is a light year

Answer 8

Some of them have exploded, and we don't know it yet. We see supernovas millions of light years distant. Stars that were long gone before we descended from the trees may announce themselves tomorrow.

Answer 9

Yes, if a star suddenly dies now and it is 300 light years away, we wouldn't see it die until 300 years later. If we saw a star 300 light years away die today, it really died 300 years ago. So what? Stars live many millions of years, or even billions years.

Answer 10

Nearby Stars (within 200 light-years): Parallax
Parallax is the apparent shift in an object's position due to a change in the observer's position. It's the same phenomenon that allows us to use our stereovision to judge distance. Because our eyes are a few inches apart, each sees a slightly different image. Try holding your thumb up with your arm fully extended and look at it first with one eye and then the other - it appears to shift position against the background. The brain uses the different views to judge the distance to the object.

Astronomers employ the same principle, using the diameter of the Earth's orbit as a baseline (like the distance between our eyes) to triangulate distances to stars. Photographs of a star taken at opposite points in our orbit (6 months apart) are compared. A nearby star will appear to have moved slightly against the background stars. The tiny angular shift of the star relative to a known distant object (such as a galaxy) provides the apex angle of a right triangle whose base is the radius of the Earth's orbit (1 AU). The distance to the star is then calculated by trigonometry (1 AU divided by the tangent of 1/2 of the angular shift). A picture will help: check out the explanation on NASA's "Star Child" web site or Professor Richard Pogge's animation.

Answer 11

Certainly some of the stars we see have probably died, but that information hasn't gotten to us yet. *shrug* That's just the way the world works.

Whenever you look at *anything*, all you see is the light from that thing and not the thing itself, so stars are no different.