Mädler attended Humboldt’s lectures while studying at university, gained his attention, and was introduced by him to the wealthy amateur Beer. Beer invited him to join him in using his private observatory; the two produced maps of Mars and the Moon of unprecedented accuracy (Mädler doing most of the hard work). Encke, another of his university teachers, got him an unofficial appointment at the Berlin observatory when Bode (who had also taught him) retired. He showed his Mappa Selenographica to Humboldt and Herschel (and pipped the latter in first using the word ‘photography’), and corresponded with Gauss.