E. Pickering detected IC 434 photographically in 1889, the Horsehead can
be detected on a photo made on January 25, 1900 by Isaac Roberts
(Roberts 1902). E.E. Barnard recognized the
object in the 1910s.
The first published description of the Horsehead Nebula was given in
Barnard (1913), and it was first cataloged by
Barnard (1919).
The remarkable Horsehead is a dark globule of dust and non-luminous gas,
obscuring the light coming from behind, especially the moderately bright
nebula IC 434. It is the most remarkable feature of an
interesting region of diffuse nebulae, which belongs
to a huge cloud of gas and dust
situated 1,600 light years away in the direction of constellation Orion.
The bright reflection nebula in the lower left is NGC 2023.
Isaac Roberts, 1902.
William Herschel's observed Nebulous Regions, 52 in number, compared
with Isaac Roberts' photographs of the same Regions, taken
simultaneously with the 20-in. reflector and the 5-in. Cooke lens.
Monthly Notices of the Royal Astronomical Society, Vol. 63, pp. 26-34
[ADS: 1902MNRAS..63...26R]
Has the "discovery photo" of the horsehead. Roberts mentions this dark
nebula in his description as "an embayment free from nebulosity
dividing it [IC 434] in halves."