In 1984, Wolfe retired from his engineering position and was then able to devote more time to his writing. In the 1990s, Wolfe published two more works in the same universe as "The Book of the New Sun". The first, "The Book of the Long Sun", consists of the novels "Nightside the Long Sun" (1993), "Lake of the Long Sun" (1994), "Caldé of the Long Sun" (1994), and "Exodus From the Long Sun" (1996). These books follow the priest of a small parish as he becomes wrapped up in political intrigue and revolution in his city-state. Wolfe then wrote a sequel, "The Book of the Short Sun", composed of "On Blue's Waters" (1999), "In Green's Jungles" (2000) and "Return to the Whorl" (2001), dealing with colonists who have arrived on the sister planets Blue and Green. The three "Sun" works ("The Book of the New Sun", "The Book of the Long Sun", and "The Book of the Short Sun") are often referred to collectively as the "Solar Cycle".