The famous "Horsehead" Nebula is a dark cloud of interstellar matter consisting of organic materials which, during the last decade of the 20th century, were determined by astrophysicists to consist of small particles similar to cigarette smoke, according to Dr. Alexander Tielens of NASA-Ames Research!

The Horsehead was discovered and measured by Mrs. Williamina B. Fleming on a photographic plate of the Orion region taken by William Pickering at the Harvard College Observatory in the 1880s. For information on the history of the discovery of the Horsehead, please refer to our Horsehead Project website. The Horsehead nebula was given the catalog number "B-33" by Edward E. Barnard in his catalog of "349 Dark Objects in the Sky". According to our research, the Horsehead became colloquially named sometime prior to 1923, due to the cloud's similarity to the head and neck of a horse as seen against the faint light of a large hydrogen-gas nebula, IC-434.

Color photographs register the lovely red color of H-alpha light wavelengths of IC-434 (at 656 nanometers wavelength), but to the human eye this faint energy is absolutely invisible in most amateur-sized scopes, due to the "Purkinje" effect. But, the eye can detect the weaker greenish-blue H-beta line at 486.1 nm; thus IC-434 appears as a faint greyish glow, with the Horsehead perceived as a very dark spot only about 1 by 5 arcminutes in size, or even less depending on the efficiency of the scope, superimposed on the pale background.

Without a filter, a telescope of about 15-17" in the darkest of skies may reveal the H-beta radiation of IC-434 when the object is at the meridian at the highest possible elevation, under the best conditions of "seeing", but the Horsehead often remains virtually invisible. But by using a hydrogen-beta filter employed with an exit pupil of 4-7 mm, the contrast of IC-434 is increased by diminishing most other wavelengths. Then the dark foreground of the Horsehead cloud may be seen even in apertures as small as 7-8 inches with careful scrutiny, and some amateurs have been able to spot it with smaller telescopes. For more information, consult our web article on using nebular filters, and our observing guide to the Horsehead nebula.

The photograph of the Horsehead Nebula that has provided the basis for the two simulated views was made by Ryan Wood (then only 14 years of age!), employing an 8" aperture f/5.2 telescope at prime focus, with a broadband LPR filter, using Kodak Ektapress 1600 film, sensitized with forming gas. Exposure: 40 minutes.

PICTURE NO. 1 (left): A simulation of the view of the Horsehead Nebula region in a 17.5" scope at moderate magnification under a sky with about 6th-magnitude naked-eye stellar limit, and using no filter. With lots of imagination, one can almost detect the Horsehead's pale outline.

PICTURE NO. 2 (middle): The second image of the Horsehead is a simulation of the image under the same conditions, but with the contrast enhancement provided by using an EXTREMELY narrowband hydrogen-beta filter at the correct exit pupil for highest contrast of the dark cloud against the faint IC-434 background. The Horsehead is perceived as a discrete dark patch against the gray, dim background glow.

PICTURE NO. 3 (right): The original color image, photographed by Ryan Wood with his 8" f/5.2 telescope. A color print was scanned at 600 dpi and converted to a 320x200 256-color file, with a small amout of computer processing to enhance contrast and sharpness. The image was also scanned in monochrome and converted to high-resolution 640x480 16-level grayscale images, and processed by Steve Waldee with "Photofinish" (tm) by ZSoft and "Neopaint" (tm) by Neosoft. Special effort was made to diminish the high contrast of the photograph to present the image as the pale, delicate view seen by eye under excellent conditions, as aided by the hydrogen-beta nebular filter. This version of the picture, done in the early 1990s, was used in "Eyepiece" but is not nearly as good as a modern re-scan of the original, done in 2005 by Ron Wood, which you may see by clicking here.