A Section of the Constellation Cygnus (August 13, 1885), Paul and Prosper Henry (x)
Astronomers at the Paris Observatory, the brothers Paul and Prosper Henry inherited in 1872 a project begun twenty years earlier—the mapping of the heavens by means of painstaking observation, calculation, and notation. In a dozen years they charted nearly fifty thousand stars. When, in 1884, their survey approached the Milky Way, the Henry brothers found that the cluster of stars proved far too dense and complex to chart by eye, and they constructed a photographic telescope to produce an exact, objective record of the sky.
