- Blue supergiant (Wikipedia)
A blue supergiant (BSG) is a hot, luminous star, often referred to as an OB supergiant. They are usually considered to be those with luminosity class I and spectral class B9 or earlier, although sometimes A-class supergiants are also deemed blue supergiants.
- Siderian (Wikipedia)
The Siderian Period ( /saɪˈdɪəri.ən, sɪ-/; Ancient Greek: σίδηρος, romanized: sídēros, meaning “iron”) is the first geologic period in the Paleoproterozoic Era and lasted from 2500 Ma to 2300 Ma. Instead of being based on stratigraphy, these dates are defined chronometrically.