Why don’t we constantly see new stars in the sky as an increase of light travels to us?


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 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.

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.