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

Redshift only works/becomes noticable once we pass the area where z = 1. (Which is a diameter of 10 billion light years from any single point) For some reference, star A which is 3,500 K lower than star B at the same distance would both have false interpretations/sightings after they’ve passed 10 billion years in d away from say Earth.