with how light works and the constant expansion of what we term the “observable universe” why don’t we constantly see new stars appearing in the night sky as the observable part expands and stars/galaxies light reaches us for the first time?
The night sky has stayed relatively the same (accounting for changing postions over time, stella phenom, supernovas etc.) for all of humans written history.
In: 515
It does change a lot, our life span is just too short to notice. It’s like looking at a single frame of an endless movie.
The observable universe isn’t actually expanding, it is shrinking!
Our observable universe is determined by what light has had time to reach us from distant parts of the universe. In a static universe with a specific start time this would mean that we would continually be seeing more universe as this shell expands at a rate of one light year per year. However the universe isn’t static, it is expanding in volume equally across space. As a result over larger distances this expansion increases in speed, to the point that at the very edges of our observable universe the expansion outstrips the speed of light! The amount of stars in the universe we can observe then is shrinking because space is appearing between the stars faster than light can cross it to reach us.
Edit: The other big issue with your question is that what we can observe in the sky with the naked eye is almost entirely within our own galaxy. We can see some nearby galaxies and star clusters as faint smudges, but overall the vast amount of the observable universe isn’t something that would impact our view of the night sky regardless of if it was expanding or shrinking.
Stars are really old, like billions of years. So is the universe. It takes a long time, millions of years, for stars to form. You’ve been alive for less than .001% or less of the time it takes for new stars to form.
Star time is a bunch longer than human time.
The only stars we can see are pretty much in the Milky Way. Any further and they are too small to be seen.
The Milky Way creates around seven stars a year, but bear in mind that 90% of all stars are red dwarves, again too small to be seen with the human eye.
The stars that are far enough away for us to not have seen them by now are *so* far away that they are incredibly feint. Those stars are *far* too faint for you to see with your own eyes.
But also, the [observable universe is shrinking](https://medium.com/swlh/the-universe-is-expanding-but-its-also-shrinking-4bcb1b6c7c8f). The whole universe is expanding, of course, but because the expansion is accelerating and because the edge of the observable universe is so incredibly far away, the most distant galaxies are receding away from us faster than light. Galaxies beyond a certain point are too far away for us to *ever* see them because the space between us has already been expanding faster than light so that their light never had a chance to reach us.
As the universe has continued to expand faster and faster, more and more galaxies will cross that line so that their light can’t reach us anymore.
It takes millions of years for stars to form and die. In order for us to even be able to see most stars, they need to already be inside of our galaxy, so its not like a new star forms or dies in our galaxy every day. When you get further out, there are distant galaxies that you can really only see with high-tech telescopes. We can see supernovae all the time from those distant galaxies, but not with the naked eye.
When the Hubble Telescope first started taking pictures of deep space, we just pointed it at an empty patch of sky to see what would happen, and we were amazed by the number distant galaxies we could see that we would never be able to see from Earth.
There are a couple of recorded supernovae that happened in our galaxy, though. It would appear in the sky as a very bright “new” star for a few days/weeks. About a dozen in the last 2000 years.
The sky also does change as the stars move around the galaxy, but not much over the last few thousand years (when humans started recording the positions of stars in the sky). About 10000 years ago, the North Star was actually Thuban, not Polaris.
Well, to be frank this has/ is happenning. Except that on a cosmic scale, the stars and galaxies become visible slowly over eons. Human history simply isn’t long enough for a noticeable change. Go back 10,000 years, the night sky is different, but not so much that you’d not be able to recognize constellations. Go back to the time of the dinosaurs, some 64 million years, and the sky look drastically different, with different stars shining, different galaxies beingvisible. Many starts shining then have long since burned out by today. Like wise many stars visible today weren’t even around back then.
Your other question is why can’t we see more of the universe as it continues to expand. That somehow there’s this greater unseen galactic mass. In reality, thanks to the background radiation mapping, we have a good idea of the expanse of scope of the universe. The observable universe isn’t so much what can be seen and then there’s this whole ocean of space just beyond the horizon as much as it is, the part of the universe that can be seen, measured, or studied, vs the portion of the universe that simply can not me seen measured or studied, but we can still observe a measured impact from that other part to know it exists. Dark matter.
Further, as the universe continues to expand, amd objects continue to shift away from one another, we will slowly begins seeing g fewer and fewer stars, not more. One theory of expansion has the universe spread so thin that the night sky becomes void of everything aside from local interstellar bodies. Lonely, but likely the fate of the universe if it’s still around.
2 things. The stars are so far away that you can’t see them with the naked eye and when you use a telescope you can see many more but still in the dark they are just too far to be able to see. But light still gets to us from really far away.
Second, there is a theory that the universe is expanding exponentially faster, so quickly on the edges of space that it is expanding faster than light in fact. For this reason the sky is not filled with light. Imagine chasing a bike while running 10 mph. But the bike is going 11 mph. You will never catch it and it will keep getting further. Away
The expansion of the universe takes distant galaxies away from us at faster than the speed of light, so they never enter the observable universe .
If you keep walking down a road will you eventually see that truck that passed you 20 minutes ago? (If it didn’t stop)
Something like 99% of the stars you see in the night sky are in a small patch around us within the Milky Way. Beyond that would be brighter stars still within the Milky Way. We cannot see stars alone outside of our own galaxy.
The nearest major galaxy to us is the Andromeda galaxy with an estimated 1 trillion stars and approximately 2.5 million lightyears away yet you can barely just see this massive space structure (natural structure, I’m not a crazy person saying it was made by beings) with the naked eye due to this huge distance.
If you can barely see an object made of 1 trillion stars you’ve no hope of seeing the individual stars within it. It’s like seeing a grain of sand a few feet away and hoping you can see the atoms that make it.
Now the edge of the observable universe is around 46.5 billion lightyears away. That is 18,600 times further away from us than Andromeda.
If we can barely see Andromeda, a space structure made of 1 trillions stars, how would we have any hope of seeing a star that is 18,600 times further away.
I hope this has explained it easily enough for you.
I think most people tend to forget or just don’t know just how incredibly huge space is. Here is a video to help show the sheer size of space, I love to watch it at least once a year by reallifelore
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