Located about 2 degrees south of the Orion Nebula is NGC 1999, a classic reflection nebula illuminated by the lone star, V380 Orionis. The nebula lies in the Orion "A" molecular cloud complex and is notable for a dark T-shaped cavity located centrally in the nebula, about 20 arc seconds southwest of V380 Orionis. The small dark cloud is designated "Parsamian 34" and its nature is controversial. It was previously believed to be an example of a "Bok globule," named after the late University of Arizona astronomer Bart Bok. More recent studies suggest it may in fact represent a peculiar shaped empty cavity within the reflection cloud. The spectrum of the central star and the nebula are identical which tells us that what we see is truly reflected starlight. At visual wavelengths the blue light we see is scattered by microscopic dust grains as small as 0.2 to 0.5 microns. The blue light has a similar wavelength as the dust particles and is scattered more efficiently than the longer wavelengths of light. The reflected starlight therefore produces the optical appearance of a brilliant blue nebula.
The geometry of NGC 1999 is that of a star centrally imbedded within a dense cloud of dust. V380 Orionis lies approximately 1/3 of a light year deep to the surface of the cloud as seen by the observer. V380 Orionis is a pre-main sequence B9 white star known as a Herbig Be star. It has a mass 3.5 times that of our sun. These intermediate mass (2 to 8 solar mass) pre-main sequence stars are defined by their association with dark nebulosity and specific spectra. There are many similarities between V380 and another Herbig Be star, HD 200775 the illuminating star of NGC 7023 (see NGC 7023).
Two bright Herbig-Haro objects exist nearby to NGC 1999. They are designated HH-1 and HH-2 and represent the first of these objects recognized by Guillermo Haro and George Herbig around 1950. The nature of these objects was unknown to Herbig and Haro at the time they first catalogued them. We now know they are shock excited nebulae. The small glowing clouds are the result of energetic outflows ejected from low mass protostars hidden from view by thick clouds of dust. The outflows from these infant stars power shock fronts that collide with the ambient gases and dust at speeds exceeding 100,000 miles per hour. The heated ambient gases then release the newly acquired energy in the visual wavelengths and appear as a deep and eerie red glow. Herbig-Haro objects are found most often in areas of active star formation. HH1 and HH2, although catalogued separately, are really part of the same structure, being opposite ends of a bipolar jet of superheated plasma ejected from a single low mass protostar. NGC 1999 is located in a fertile region of low mass star formation. Infrared instruments have detected several young clusters of stars hidden from optical view behind the dense dust clouds surrounding NGC 1999.