Helliconia Summer (Helliconia Trilogy‪)‬

The Grand Master of Science Fiction's "monumental" epic continues as Helliconia nears its larger star—and a strange visitor joins its civilization (The Times, London).

A handful of centuries on, Helliconia is close to the larger star in its binary system, and the Phagors have been driven into exile, but conflicting religions and hostility to science keep human civilization fragmented and constantly fighting wars over petty power and fertile land as a plague devastates populations. However, everything changes when a secret visitor from the observer satellite from Earth accepts a slow death in order to visit the planet and spend his time in the sunlight and open air.