I was watching carl sagans cosmos and there is an episode where he talks about a planet outside the milky way will have not a sun rise but a galaxy rise when it rotates and the galaxy comes into view a sky filled with billions of distant suns but it got me thinking, we cant see most of our galaxy right? because the stars are too far away, so the light has been redshifted out of the visible spectrum wouldnt a distant planet lose the view from alot of the stars aswell so it wont be that strong?
We can't see most of our galaxy because we are in our galaxy, and all the dust and such in the spiral arms blocks our view.. not just of our own galaxy, but the billions of other galaxies. But a rogue planet just outside of the galaxy would be able to see most. It's much like the Andromeda galaxy.. if you live in a good place for it, you can see the Andromeda galaxy with the naked eye, from Earth. It takes up about 6 times the night sky than what the moon does. Also, the stars within our galaxy can't be seen due to them getting redshifted. We can see billions of galaxies outside of our own galaxy.. that are thousands of times further than any star within our galaxy. I believe it is something like 14.5 billion light years that will be visible to us. Anything outside of 14.5 billion light years will not be visible due to its light getting shifted out of the visible spectrum. The furthest star away from us in our galaxy would be but a fraction of that 14.5 billion light years.
By visible spectrum you mean visible to our instruments, not to our eyes? Just to clarify for OP. Also, it seemed you agreed with OP but I don't think you meant to. I reread it a few times but maybe I am missing it. You are telling OP that the stars in our own galaxy would NOT be redshifted to the point where we couldn't see them, since we can see stars from much further away (correct)?
Yes, I meant shifted out of the visible spectrum. If a galaxy is 13 billion light years away, it's light is going to get redshifted a good bit by the time it reaches us. It'll still be in the visible spectrum.. and if we had eyes with a good enough resolution, we could see them without the aid of a telescope. Thing is, around 14.5 billion light years.. the rate of expansion relative to us surpasses the speed of light. So any galaxy beyond that point will never be see by us. If there were a galaxy that is something like 14.4 billion light years away.. it's light will get shifted a great deal and the light energy will get shifted so much, that it's no longer technically light.. more like microwaves. My personal theory is that is actually where the cosmic background radiation comes from, but that's a whole other topic. Stars within our own galaxy though.. they're not far enough away to be redshifted to the point where we can't see them, not like with distant galaxies. Our galaxy is only 100,000 light years across. The reason we can't see all the stars in our galaxy is because of the amount of cosmic dust blocking our view. Now if the light from a star in our galaxy travels to us and through all that dust.. we can see a redshift effect, much like the redshift effect we see when the sun sets and rises. I don't think "they" technically consider that to be redshift though.. as it is caused by the scattering of light. Think of it as if you were in the middle of a forest. When you're in the forest.. there are so many trees, that trees block your view of other trees. There are going to be countless trees that you physically can't see.. because you are in the forest. Now if you hopped on an airplane and flew over the forest, you'd be able to see so many more trees. That's how it is with us and stars.. we are in a giant disk of dust and plasma and stars and planets and all sorts of stuff, and most of it is just simply blocking our view. So yes, a quick n easy explanation as to why stars in our galaxy can't be redshifted to the point where we can't see them is because we are able to see objects many many many times further away. There is a distance factor to take into consideration, and all the stars within our galaxy are well within that distance. As for the actual question.. guess I did miss that.. but yes, a galaxy rise is completely possible. Planets more than likely don't form outside of a galaxy.. but due to a disaster, could get ejected out of a galaxy and become a rogue planet. Chances are any complex life on it would die by the time it makes it out of the galaxy.. but if something did survive on it, there is a good chance that it would witness galaxy rises and sets.
would the main star of that rogue planet cancel out the galaxy-rise? Or would the brightness of the combined galaxy be enough to shine through the planet's star?
If the whole star system was like ours.. but if a planet somehow gets knocked out of its orbit, it probably won't have a star. We are pretty sure that there are planets out there without a star to belong to. For a variety of reasons.. but there very well could be a planet that is stuck outside of a galaxy without a star. Plus.. you're looking at it from an Earth PoV. If you were sitting on Pluto.. or any of the other planetoids and possible planets beyond Pluto, the sun doesn't look that much different from all the other stars. I don't see it as impossible for a star and planet combo to exist outside of a galaxy.. and if it were like here on Earth, their sun would probably block out the galaxy. If the planet were between the star and the galaxy.. it could have a sun set followed by a galaxy rise followed by a galaxy set followed by a sun rise followed by a sun set and so on.