How to know if stars that we look at are still there?

Answer 1

if u r already looking at a star, then there is no point of the star not being there.......

Answer 2

No easy way. The light that is coming from a star 50 light years will take 50 years to get to us, so if anything happened to that star now, we would not know until 50 years from now.
That said, stars are relatively predictable. We know, for instance, that a star like our sun is about halfway through its life, and that it will take another 4 or 5 billion years before its core exhaust its hydrogen and has to start fusing helium instead, turning it into a red giant.
So, although we do not know if a star is still as it seems to us now, there is also very little chance that it would NOT be the same then as it seems to be now.

Answer 3

It is possible to characterize the star as to magnitude and distance. Based on the magnitude of the star (relative to the star sequence) it is possible to estimate its life in which case huge stars burn up their hydrogen fuel much faster than smaller stars. This should allow an estimate as to whether the star has reached the end of its life by the time the light being observed now has reached earth.

Answer 4

We don't know for sure, but we can identify the stellar type by analysing the light, and stars follow a pretty predictable sequence of evolution, usually plotted on what's called the HR diagram. So we can state with some confidence whether a star is stable or not, and so if it is likely to have gone Nova or burnt out.

Answer 5

The short answer is that we don't. Stars are so far away... that it takes years / decades / centuries for the light to get here. If you pointed to a star that was 100 light years away, and at that very instant, it exploded, it would be about 100 years before you 'saw' it. (I say about because there might be some sort of indication, or ray of some sort that would change).

The universe is sure big!

Answer 6

Stars rarely if ever blow up prematurely. So if we know that a star is within a hundred light years and is still fusing hydrogen (which is easy to do) its still there. Farther out it gets more problematic. It is one of my wishes that we will be able to see a large supernova with the naked eye. It could happen tonight. We are about due mathematically.

Answer 7

we dont..example; the sun is a star and if the switch was turned off right now, it would be about 8 minutes before the light went out here because it takes that long for the light to travel to us. I think the next nearest star is in the Andromeda galaxy which is about 4.5 light years away, so it would be that long before we noticed any lights out.

Answer 8

Hi >
I agree with the above answers.
We simply cannot be certain, due to the time it takes electro-magnetic radiation, which includes visible light, to travel from A to B. Hence we look at star, as you mention, say 100 ly away,it may not be there anymore, although that is unlikely.
I have had a word with my God, and he/she is not too sure either.
Hey Ho.
Bob the Boat.

Bob.

Answer 9

Agree with others (you can't know). Also, I think your question presupposes there is some universal background clock shared by all objects in the universe, by which we can gage elapsed time between spatially separated events (star blows up over there right "now", then we see it blow up here at a later "now"). Not the case. Different observers will disagree on the elapsed time between the events, and some may think they are almost simultaneous.

Answer 10

You have to wait for light to reach earth. Say a star that's 100 light yrs away expodes, we won't know until 100 yrs after the exposion. In other words, impossible to till from earth until the light reaches us.