Free Astronomy Magazine May-June 2022

4 MAY-JUNE 2022 ASTRO PUBLISHING into space, it goes without saying that Population I stars are typically younger than those in Population II. The Sun, although not very young (4.6 billion years), belongs to Population I, which sug- gests that Population II stars must be older on av- e r age . I n the first decades of the last cen- tury, astronomers realized that stars could essentially be divided into two populations based on the abundance of metals found in their spectra. It was Walter Baade, in the 1940s, who proposed the Spartan subdivision (still in use today, with some variations) into Population I stars and Population II stars, the for- mer rich in metals (2-3% of the mass), the latter poor in metals (0.1% of the mass). Since the metallicity of the universe has increased with the passing of billions of years due to the produc- tion of metals in stel- lar nuclei and their sub- s equen t spillage Earendel and the universe of the Population III by Michele Ferrara revised by Damian G. Allis NASA Solar System Ambassador O bservations from the Hubble Space Telescope, pictured here, allowed a team of researchers to discover what is now the most distant star in the universe, Earendel. Towards the end of this year, Hubble’s successor, the Webb Space Tele- scope, will analyze the light from that star, and we will determine if Earendel belongs to the elusive Population III. [ESA/Hubble]