Also Known As: Barnard 33, LDN 1630, Horsehead Nebula
Object Type: Emission Nebula + Dark Nebula
Right Ascension (2000.0): 05h 40m 59.0s
Declination (2000.0): –02° 27' 30"
Dimensions: 60' x 10'; 6' x 4'
Distance: 1,500 light years
Discovery: William Herschel, 1 February 1786 (18.7" Reflector)
NGC Description: neb, 60' l, south from Zeta Ori
Telescope: Parks Astrolight EQ6 • 6" f/6 Newtonian Reflector
Eyepiece/Magnification: 15mm Parks Gold Series Plössl • 60x • 52' FoV
Date/Time: 14 February 2010 • 04:00-05:00 UT
Observing Location: Oaksanita Springs, Descanso, San Diego Co., California, USA
Transparency: NELM 6.3, TLM 14.2
Seeing: Pickering 8
Conditions: Clear, calm
One of the most elusive grails of visual astronomy is the fabled Horsehead Nebula, a protrusion of dark nebulosity superimposed on a gossamer veil of exceedingly faint nebulosity dangling from the easternmost star in Orion's belt known as IC 434. It has been quite a few years since I last observed this object and it proved to be as difficult as ever.
The only thing easy about the Horsehead Nebula is finding the correct location. Center your scope on second-magnitude Alnitak (Zeta Orionis) and sweep a mere ½° south; the object of your search (believe it or not) is now in your field of view, and if you are at a dark sky site on a moonless night, you might catch a glimpse of this emission and dark nebula combination.
Make sure that the blinding glare of Alnitak is removed from the field of view (I achieved this by selecting the 15mm Plössl, which provided a good compromise between low magnification and a small enough field of view to exclude the bright star). If the Horsehead is still not readily visible, carefully examine the background sky visible through your eyepiece and see if you can discern that the western half of the field is subtly brighter than the eastern. Gently move your scope from east to west and back again to pick up the relatively sharp western edge of the IC 433 HII region. Once you have identified this edge between the dark and not-quite-so-dark halves of the field of view, look for a small notch or gap one third of the way from HD 37805 to HD 37806, a pair of 8th magnitude stars separated by 24' and aligned north-south.
The emission portion of the nebula (IC 433) is likely ionized by the blue giant star Sigma Orionis and is estimated to lie at a distance of 1,500 light years. William Herschel discovered this object on February 1st, 1786. The dark nebulosity, which makes this region so famous, was catalogued by E. E. Barnard as the 33rd object in his famous catalogue of dark nebulae, published in 1927. Its first treatment in the professional literature can be traced to Barnard's 1913 Astrophysical Journal article "Dark regions in the sky suggesting an obscuration of light." Barnard's three paragraph description of the as yet unnamed and uncatalogued object is worth reading. You may review the actual article here (see pages 500-501, beginning at the midpoint of page 500).
An additional object of interest may be found in the same field of view. This is the reflection nebula NGC 2023 surrounding the star HD 37903. This nebula is surprisingly prominent (way easier than the Horsehead) and, in my opinion, one of the best examples of a reflection nebula for the visual observer. It exhibits a satisfying amount of structural detail and takes magnification well. Be sure to check out this overlooked object next time you're in the area.