My title is a pun on Stravinsky's characterisation of Pierrot Lunaire as the solar plexus of twentieth-century music. Given its place in the history of musical depictions of moonlight, I characterise Pierrot as the twentieth century's lunar nexus - a place of intersections among literary and musical depictions of moonlight in the nineteenth and early twentieth centuries. The first part of this essay is a survey and discussion of the musical topos of moonlight in German and Austrian nineteenth-century literature and music. I then discuss Schoenberg's depictions of moonlight in key works prior to Pierrot, including Verklärte Nacht, Gurre-Lieder, Pelleas und Melisande and Erwartung. The third section explores the depictions of moonlight developed across the 21 songs of Pierrot, with special focus on three: 'Mondestrunken', 'Eine blasse Wäscherin' and 'Der Mondfleck'.