here. Poul Anderson's novel about an extra-solar craft entering the Solar System is The Byworlder, which maybe I should reread. I remember that a non-humanoid alien is in orbit while various things are happening on Earth. That is all. Rereading an Anderson novel from sufficiently long ago always generates new blog posts.
"Da capo" means "from the beginning";
a late chapter in Olaf Stapledon's Last And First Men is called "Da Capo":
the last "story-to-be-told" in Robert Heinlein's Future History was called "Da Capo";
Heinlein's Time Enough For Love also ends with "Da Capo" although I do not accept this volume as a valid continuation of the Future History;
the concluding volume of James Blish's Cities In Flight future history is The Triumph Of Time;
the last story in Poul Anderson's Psychotechnic History is called "The Chapter Ends."
There is a conceptual continuity between future histories.