If you saw stars that were 20 light years away?

Question

Doesn't that mean that the light from the star left 20 years ago? And that the star you are seeing right now, was actually what it was 20 years ago?
If that's true, then half of the stars seen in the sky don't exist anymore!
Isn't that right?

Answer 1

>Doesn't that mean that the light from the star left 20 years ago? And that the star you are seeing right now, was actually what it was 20 years ago?

That is correct.

>If that's true, then half of the stars seen in the sky don't exist anymore!

Why? Most stars last for hundreds of millions of years. It would be EXTREMELY unlikely for so many of them to burn out within the time it took their light to reach us. Besides, the whole nova process takes a few million years by itself (at least for main sequence stars like the Sun), so if a star was 20 light years away we'd only see it in the stage of its nova 20 years before what it's actually at.

Answer 2

Most the stars we see are relatively close - within, say, 1000 lightyears. Much further than that, and they're too dim to get through our atmosphere (there are exceptions, of course).

Probably the furthest object we see with the naked eye is the Andromeda galaxy, which is about 2.3 million light years away - so, in effect, we're seeing it as it was 2.3 million years ago.

I'd guess a few stars we see now don't exist anymore, but... 1/2? That's a pretty big number.

Answer 3

Most of the stars that we see (with our eyes, not with a telescope) are within the same spiral arm as our Sun. At most, the stars that we see are a few thousand light years away.

We do not see individual stars from other spiral arms in our own Galaxy nor from other galaxies. If we do see anything, it is the total glow of millions of stars (e.g., the Milky Way).

Most stars that we do see are very massive stars that use up their fuel very fast. Many will only live for a few million years (instead of billions).

By comparison, most stars that we know to exist are too faint to be seen from very far (our own Sun would be invisible to us from fifty light-years -- unless we used a telescope, of course).

Still, a life-time of millions of years against a distance of mere thousands of light years means that in all probability, less than 0.1% of the stars we see don't exist anymore.

Answer 4

Yes, the light you see left the star twenty years ago...I don't know about half of the stars being gone, but since the average age of a star is in the order of ten billion years or so, the star that are that far away have a high liklihood of being transformed...

Answer 5

You are correct that the light has traveled for 20 years to reach us. But as far as we are concerned, we are seeing the star as it is "now". There is no absolute temporal reference point.

The average star lives for billions of years, and spends a long time dying. So it's extremely unlikely that any of the ones you are looking will die in the length of time it takes the light to get here. The one exception is probably eta Carinae in the southern hemisphere, which could go supernova any time.

Answer 6

It was believe to be here in Vegas in Area 51 a bit long time ago, but I don't think the aliens gather around there anymore. I mean, people are guarding the area. I do believe aliens exist, but not in the way people make them come alive in movies and stuff. I've not seen an alien come up to me and look at me, but I have seen an image of it: On a Saturday morning, in my mom's bedroom, she woke up and she was lying down in bed, when she saw on the ceiling, the perfect shape of an alien! This is true and she freaked out. Why would it show up that day out of the days? Afterwards, the "alien" disappeared after some days. I'm serious, it was the perfect shape of an alien up in the ceiling. It didn't look green, but the shadow looked grayish. We checked it it was the shadow of something inside the room or outside the window in the curtains, but we don't think it was the shadow of anything. It was freaky, but yeah, that's my story. I do believe in aliens. Just how humans live on planet Earth, I say in other planets there exist some sort of others. Either aliens, some other sort of creatures... I mean, you never know for sure, do you?

Answer 7

We can't say they don't exist anymore, just that we don't know what they look like right now. If we see one go supernova right now, it actually exploded years ago.

The closest star besides the sun is Alpha Centauri, at 4.3 light years. So we can't tell whats happening with that right now, until 4 years from now!

Answer 8

that is a weird concept , so what we are seeing is not actually whats occuring, not that the star doesnt exist anymore

Answer 9

You are right.
What ever we are seeing in the sky now has actualy occured 4.3 to 430000000000000000000000000 years ago.

Answer 10

i dunno about half, but mostly what you see is close or really bright. The distant stars you see are probably dead yes.