eli5: Colder stars are usually red, hotter ones are more blue. But how do scientists how much “redness” is from the star itself and how much is due to the red shift of the expanding universe?

Question

eli5: Colder stars are usually red, hotter ones are more blue. But how do scientists how much “redness” is from the star itself and how much is due to the red shift of the expanding universe?

In: 20

Answer 1

The stars we can see in the night sky are so close (on an astronomical scale) that the red shift is too small to have a noticeable effect on the color. At a distance where it becomes noticeable you can only see full galaxies and not individual stars.