The advent of deep photographic imaging allowed Edward Barnard to produce the first images of dark nebulae silhouetted against the background star field of the galaxy, while the first actual detection of cold diffuse matter in interstellar space was made by Johannes Hartmann in 1904 through the use of absorption line spectroscopy.
O advimento de imaxes fotográficas profundas permitiu a Edward Barnard obter as primeiras imaxes de nebulosas escuras perfiladas sobre o campo de fondo de estrelas da galaxia, mentres que a primeira detección real de materia difusa fría no espazo interestelar fíxoa Johannes Hartmann en 1904 utilizando espectroscopia de liñas de absorción.