The young bluestarHD 37903 lies within the fringes of the vast dark Orion Molecular Cloud that fills much of Orion. In the region around the star, the hydrogen of the Cloud is illuminated to create this roughly circular patch of blue-white light near the base of the Horsehead Nebula.
The nebula represents a small part of the vast dark Orion Molecular Cloud, visible because it reflects the light of new stars forming in this region. The result is an approximately circular area some ten arcminutes across (that is, its diameter is about a third that of the Moon's disc in the sky). In reality this nebulous region covers a region of space some 4½ light years across.
The blue-white light that illuminates the Lump Star comes from the newly-forming stars within it. There are about twenty of these stars and protostars, but the light of the nebula is primarily generated by a star designated HD 37903. This is a very young blue star, still enveloped in the gases of the Lump Starnebula where it came into existence.
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