Two Men Contemplating the Moon - 1825-30. Caspar David Friedrich / The two men contemplating the sinking moon have been identified as Friedrich himself, on the right, and his talented young colleague August Heinrich (1794-1822). The mood of pious contemplation relates to fascination with the moon as expressed in contemporary poetry, literature, philosophy, and music.
These two men had the same name, were sentenced to the same prison and look like twins. However, they were not related but are the reason that fingerprints are now used when fighting crime. (quote from CDAN)