Life as we know it developed on a planet orbiting a G2 V star, the Sun. The cryptic “G2 V” designation is the Sun’s “spectral type.” Based on a star’s spectrum, astronomers group stars by temperature.

Yellow supergiant stars (YSGs) have spectral types F or G and initial masses between 10 and 40 solar masses. Most YSGs are cooling and expanding rapidly towards red supergiants (RSGs) after ...