Barnard, E. E. (1919), "On the dark markings of the sky, with a catalogue of 182 such objects", Astrophysical Journal, 49: 1–24, Bibcode:1919ApJ....49....1B, doi:10.1086/142439
Barnard, E. E. (1919), "On the dark markings of the sky, with a catalogue of 182 such objects", Astrophysical Journal, 49: 1–24, Bibcode:1919ApJ....49....1B, doi:10.1086/142439