NGC 1909 (also known as Witch Head Nebula due
to its shape), is an extremely faint reflection nebula believed
to be an ancient supernova remnant or gas cloud illuminated by
nearby supergiant star Rigel in Orion. It lies in the Eridanus
constellation, about 900 light-years from Earth. The nature of
the dust particles, reflecting blue light better than red, is a
factor in giving the Witch Head its blue color. Radio
observations show substantial carbon monoxide emission
throughout parts of NGC 1909 an indicator of the presence of
molecular clouds and star formation in the nebula. In fact
candidates for pre-main sequence stars and some classic T-Tauri
stars have been found deep within the nebula.The molecular
clouds of IC 2118 are probably juxtaposed to the outer
boundaries of the vast Orion-Eridanus bubble, a giant supershell
of molecular hydrogen blown by the high mass stars of the Orion
OB1 association. As the supershell expands into the interstellar
medium, favorable circumstances for star formation occur. NGC
1909 is located in one such area. The wind blown appearance and
cometary shape of the bright reflection nebula is highly
suggestive of a strong association with the high mass luminous
stars of Orion OB1. The fact that the heads of the cometary
clouds of NGC 1909 point northeast towards the association is
strong support of that relationship.
