Cosmic Themes

Superheroes are derived from sf because Superman is extraterrestrial. However, some superheroes are more explicitly sfnal than others, e.g., the Green Lantern is not only a superhero based in a fictional American city but also a member of an interstellar corps organized by the Guardians of the Universe based on the ancient planet of Oa. Further, the Guardians' main enemies are from the antimatter universe.

Thus, those of us who read Green Lantern comics in the 60s encountered cosmic themes addressed more substantially by Poul Anderson and James Blish (see Between Galaxies), which explains why Larry Niven later contributed to Green Lantern.

Anderson, Blish and Niven are future historians. In Niven's Known Space future history, some non-human races are expected to flee to the Magellanic Clouds before the radiation from the galactic core explosion reaches the outer edges of the spiral arms. Thus, Niven's trans-galactic reach matches that of Anderson or Blish.