So my understanding is that stars are born and die all the time with supernovae, black holes, etc. And we can see this in deep space all the time but why can’t we see that with the naked eye? Why are our constilations the same as when I was a child? If stars are born and die all the time in our universe Why don’t we have a new night sky every few decades? I know a stars life is long so not all stars will change in my life time but there’s no new ones born or no old ones that die close enough for us to see when we look up
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Well we can only see like 5000 of the stars in our galaxy with the naked eye out of like 100billion + stars. While about 7 stars get born in our galaxy each year the chances of it being close enough to be visible are pretty much nil.
Now supernova are pretty visible from far away but most stars don’t go nova. There have only been like 5 visible nova events in the past 1000 years. The rest just kindof peter out much more quietly.
Our Universe is expanding and with it the things inside. Stars radiate light. Since light travels in waves we can only see things within the visible spectrum. Through the expansion, these lightwaves are getting stretched thus „moving out“ of the visible spectrum of light. They are getting more red the further they are away from us as red light has a longer wavelength. This is called redshifting. This can Go even further when its stretched out even more into the infrared spectrum – which we cant See with our naked eye. This is also the reason why the James webb telescope takes pictures with an infrared camera. In one of those deep space Images you can Tell by the amount of red how far away galaxys are.
Another big factor is the time it takes the light to reach us. There are maybe millions of new Stars out there but we cant See them as the light is still traveling to earth. So when you look up in the Night sky you See the stars as they were millions of years ago, some of them maybe dont even exist anymore. And the Life of a Human is so short compared to a stars life. I mean the sun is like 5 billion years old and will be there for another 5 billion. So very unlikely that you will witness a new star appearing at the sky.
Stars are *extremely* long-lived. An average star has a lifetime well into the billions of years (the Sun is a relatively large star, larger stars have shorter lifetimes, and the Sun’s lifetime is ~10 billion years). Stars you can see happen to be larger and brighter than average, but even among the stars you see, the average lifetime is something like a billion years.
Since you can see perhaps a thousand stars in a very dark sky (and much less if you live in a city), that means you’d expect to see one of the thousand stars in your sky die only once every million years or so (1000 stars * 1 star / 1 billion years). Stars are born at a similar rate – that is, the number of stars in the sky is relatively stable over time – so you’d expect to see a new star roughly this often, too.
The shortest-lived stars live 30-50 times longer than humans have even existed, so seeing star death is incredibly unlikely. As for star formation, that only happens in particular regions of space filled with dense hydrogen gas, so stars won’t just appear in the sky.
The universe is *big* like, really, really, really big. What we see is almost nothing compared to what’s even in our galaxy. Stars may be born and die all the time, but that’s on a *cosmic* scale. Basically we’re staring at a single blade of grass in a gigantic rainforest. Sure, things are living and dying all the time in the whole forest, but this blade of grass we’re staring at isn’t even close to enough to see all of that.
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