Are the stars I see in tonight's sky, still really there (speed of light / distance from earth)?
回答 (17)
2016-01-22 12:13 pm
✔ 最佳答案
What you see in the night sky is only a very, very small handful compared to all the stars in the Universe. When you look up in the night sky, you are only seeing a few thousand stars out of an estimated 100 octillion (a "1" followed by 29 zeros) in the entire universe. And what you are seeing is how the star appeared in the past (how far in the past depends on the distance to the star, the closest being about 4 years ago, and the most distant 7500 years). Even our own sun is a little over 8 minutes old when you look at it (but don't look directly at it - It can hurt your eyes).And considering that the life span of the stars is billions and billions and billions of year, you can rest assured that just about all but one or two of the stars in the night sky are still there today.
2016-01-22 7:21 pm
Any you see tonight, will be there tomorrow night or next week.
The heavenly dance is a very slow waltz.
Stars have a very long lifetime, ones like our Sun about 9 billion years.
Others, like the biggest, live fast and die young, and go out in a blaze of glory at about 10 million years.
Something that astronomers try and measure is what they call their real movement, to show if they are moving in retrospect to us.
Closer stars will show more movement, Alpha Centauri and its companions will move at a slow tangent to our solar system, north to south over million's of years till it will come as close as 3.8 light years it is proposed.
But if you are like me, I keep watching each night in the faint hope that I can catch a far away one going Supernova
The heavenly dance is a very slow waltz.
Stars have a very long lifetime, ones like our Sun about 9 billion years.
Others, like the biggest, live fast and die young, and go out in a blaze of glory at about 10 million years.
Something that astronomers try and measure is what they call their real movement, to show if they are moving in retrospect to us.
Closer stars will show more movement, Alpha Centauri and its companions will move at a slow tangent to our solar system, north to south over million's of years till it will come as close as 3.8 light years it is proposed.
But if you are like me, I keep watching each night in the faint hope that I can catch a far away one going Supernova
2016-01-22 2:55 pm
You see perhaps 3,000 stars in the night sky, and most are within a few hundred up to a few thousand light years away - pretty close, really - when you consider that the Milky Way is 100,000 light years across, and other galaxies are millions and billions of light years away - most are too faint for us to see.
Of the stars that are clearly visible, only a few may be nearing the end of their 'lives' - Betelgeuse (the shoulder of Orion) is probably the best example; there's also ETA Carinae, and a few others, which we expect to collapse suddenly and explode relatively soon - but it may be 100's of thousands of years.
So... The answer is, yes, pretty much we expect all the stars we see are still there.
Of the stars that are clearly visible, only a few may be nearing the end of their 'lives' - Betelgeuse (the shoulder of Orion) is probably the best example; there's also ETA Carinae, and a few others, which we expect to collapse suddenly and explode relatively soon - but it may be 100's of thousands of years.
So... The answer is, yes, pretty much we expect all the stars we see are still there.
2016-01-22 8:08 am
Depends how far the stars are. For instance Andromeda Galaxy is like 4.2 billion light years away, means really you are looking at 4.2 billion years ago..
2016-01-24 4:39 pm
Some are and some aren't. Light has a speed and like any moving object with constant speed, will need to move a certain distance to go from A to B.
2016-01-22 7:32 pm
Yes, they have moved a bit. All stars which have ever formed still exist in some form. Most of them don't change much in the few hundred years (plus/minus) that their light has take to get here.
2016-01-22 3:03 pm
Betelgeuse is one of the shortest lived, naked eye star with a life expectancy of 10 million years. It is at a distance of 642 light years. The time it take for its light to get here is 1/15600 of its lifetime. Your brother has a life expectancy of 27,000 days. What do you think the odds are of you going on a weekend fishing trip and coming home to find him "no longer there"?
參考: [n] = 10ⁿ
2016-01-22 1:48 pm
We have no idea - almost certainly they are somewhere near where we see them even though light has been traveling for several to many years but they are also not moving that fast.
2016-01-22 10:42 am
Yes.
Every one of the stars you can see are all still there.
There are all within 1000 light years of us -- except for a handful that are between 1000 and 2000 light years.
Many of them are long lived stars like our sun -- which will go on shining for billions of years.
And many of them are giant stars - much brighter than our sun. These have lives measured in millions (not billions) of years. Such as Polaris, the polestar
And .... none of the stares that are visible to our unaided eyes have reached the end of their lives in the past 300 or 400 years. And none are expected to reach the end of their lives for 100,000 years at least.
The novas and supernovas that you hear about are all VERY distant -- mostly in other galaxies.
Every one of the stars you can see are all still there.
There are all within 1000 light years of us -- except for a handful that are between 1000 and 2000 light years.
Many of them are long lived stars like our sun -- which will go on shining for billions of years.
And many of them are giant stars - much brighter than our sun. These have lives measured in millions (not billions) of years. Such as Polaris, the polestar
And .... none of the stares that are visible to our unaided eyes have reached the end of their lives in the past 300 or 400 years. And none are expected to reach the end of their lives for 100,000 years at least.
The novas and supernovas that you hear about are all VERY distant -- mostly in other galaxies.
2016-01-22 10:26 am
Yes. Few a more than a thousand light years away which is a blink of an eye in the life time of a star. It's more likely that you died between you posting your question and me answering it.
2016-01-22 10:25 am
Most of the star visible to us is under 1000 light years, stars doesn't change that much in 1000 years.
2016-01-22 10:21 am
Some of them will have reached the end of their lifespan. Some explode in a supernova especially the large fast-living ones like Betelgeuse. some just go nova and leave a much smaller and denser core. Some grow into red giant which will happen to our sun, before they collapse into white dwarfs.
Our sun has a total lifespan of about 9.5 billion years so if we can see a galaxy 9 billion light years away there might be some stars which have already collapsed into white dwarfs at the end of their 9.5 billion year life but we see them in the early stages of their life and their light will reach us for another 9 billion years.
Our sun has a total lifespan of about 9.5 billion years so if we can see a galaxy 9 billion light years away there might be some stars which have already collapsed into white dwarfs at the end of their 9.5 billion year life but we see them in the early stages of their life and their light will reach us for another 9 billion years.
2016-01-22 10:19 am
Compared to a star's lifespan, the time it takes for the light of those individual stars that we can see to reach us is very short. So it's very likely that every single star you can see in the sky still exists today. They may have moved to a slightly different place in that time, but not by very much. In most cases not noticeably.
2016-01-22 9:46 am
The stars you can see with your naked eye are all close by in astronomical terms, and stars aren't "normal" one day and explode the next - they become unstable over a long time. Very few of the naked eye stars (I can think of 2 off the top of my head) is going to become a supernova any time soon, so it's safe to say the stars are still there.
2016-01-22 8:58 am
I do understand this guys, and I do appreciate your input. I may not have expressed my question correctly. Is there a way to know which stars are on their deathbeds? Is there a way to determine their ages and distances?
2016-01-22 8:25 am
Most of them - but the recently seen supernova died long ago.
2016-01-22 2:57 pm
Maybe not. A LOT could have happened in the hundreds of thousands of years since the light you see actually left the star.
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