In the Throne World, complete public events with a Solar or Stasis subclass equipped. Heroic public events grant additional progress.
"Okay, bear with me: I noticed that bombarding major cosmological events with extreme temperatures can make this, uh… let's call it a wobble in the fabric of the Ascendant Plane. So I'm thinking, maybe I can use that like sonar to do some scouting! Ha ha… yeah, don't ask me how I figured this out." —Fynch