Complex sentence: He spent most of his career since his youth making drawings of the Moon, and by 1868 his map of the Moon was almost ready, although he did not put the finishing touches to it until 1874.
Split into simpler sentences: He spent most of his career since his youth making drawings of the Moon, preparing a map of it. By 1868 his map of the Moon was almost ready, although he did not put the finishing touches to it until 1874.