The Horsehead Project:
19th CENTURY NEBULAR STUDIES,
& THE DISCOVERY OF THE HORSEHEAD

Introduction

As a modern astrophysical icon, the Horsehead's image graces not only the covers of academic science books, but also articles in the popular press such as a recent newspaper account of the Hubble space telescope, where the head and flank of the proud steed evoke the depths of the universe to be penetrated by the power of professional astronomy's latest tool of exploration. But what can the amateur do to learn of this challenging (and faint!) deep sky object, whose portraits required for many decades the machinery of the greatest observatories?

During some years in which I sold commercial telescopes under the gaze of the horse in the stunning poster of the famous Anglo-Australian Observatory photograph made with the 150-inch telescope by David Malin, I frequently encountered customer queries about the possibilities of viewing the nebula by eye with one of the dealer's shiny new instruments on display.

But my own early failures to find the Horsehead had been contradicted by the published reports of amateurs viewing the nebula in a variety of small telescopes. I had seen excellent amateur pictures, taken with much precise effort with expensive Schmidt cameras; but finally finally, the exceptional achievements of one of my fellow employees, teenager Ryan Wood, in photographing the Horsehead with a relatively simple, small 70mm aperture fluorite-lens telescope spurred my own decision to investigate it. I started with the discovery and early history of the Horsehead, so sparsely and inconsistently detailed in even some of the finest modern reference sources.

I had read in one book that it was discovered by "Pickering" (but, I wondered, E. C. or W. H.?); in another, the more explicit claim "William Pickering"; another asserted it was found by Barnard.1 What would the historical record of 19th century publications reveal?

As a Lick Observatory volunteer, I assist my wife, harpsichordist Regina Roper, and UC/Lick history docent W. ''Shiloh'' Unruh, in presenting the yearly "Music of the Spheres" classical concerts in the dome of the 36-inch refractor on Mt. Hamilton. My contacts at the Observatory provided me with access to the Mary Lea Shane Archives, plus much-appreciated advice from numerous distinguished former and current staff members. The renowned Lick Observatory astronomical library at the University of California in Santa Cruz provided the original source materials from which the true story of the earliest days of mankind's first knowledge of the Horsehead nebula has at last been pieced together through the months of studying the professional journals, preserved in this vast collection.

I have arbitrarily chosen to cut off this account with the first picture of the Horsehead that seems clearly beyond the capability of today's amateurs [in 1990, but not today in 2005! - srw]: the wonderful 1920 plate photographed by John C. Duncan with the 100-inch Hooker telescope at Mt. Wilson, a picture which has enduring scientific value in studying details of what we now know is an area of star formation providing evidence of physical processes on the grand scale of the universe.

After an accounting of all the earliest published photographs of the Horsehead up to Duncan's, and the resolution of the controversies swirling at the end of the 19th century about the existence of faintly luminous light and dark matter in deep space, the concluding part of our study will explore the techniques of directly observing the object with the smallest and simplest of equipment.

Here is the remarkable saga of the early period of the study of the Horsehead, involving seven male astronomers, and three influential woman investigators, who all helped solve the riddle of the great bright and dark rifts of the Milky Way, puzzling to watchers of the skies for over two thousand years of recorded science.

PRE-HORSEHEAD-DISCOVERY SIGHTINGS OF BRIGHT AND DARK NEBULAE

The giant upon whose shoulders we stand in studying the Horsehead is the amazing William Herschel (1838-1822), whose 18.8 inch and 48-inch aperture reflector telescopes could turn the dim and blurry images of cometary smudges, as seen in Charles Messier's little 90mm aperture refractor, into brilliant starry globes and diadems, or milky glowing fields of soft light.

If Herschel's painstaking calculations are accurate, he was theoretically capable of observing stars to the 17th magnitude until the moist English climate tarnished his polished "speculum" metal reflector, but his usual result achieved a limitation of 14th to 15th magnitude, which may be reached photographically by today's 10-inch aperture Schmidt-Cassegrain scopes in dark skies. A canny observer, the great German born British amateur astronomer knew how to calculate the best telescopic exit pupil for the most efficient transfer of light to his eye. While sweeping the skies during the years 1783 to 1802, he found no fewer than 52 regions affected with "extensive diffused nebulosity" that could be seen only by means of his enormous telescopes.

The nebulosity in many of his 52 regions went unstudied for nearly a century, save only by his son John, who over a period of eight years carefully re-examined his father's observations. Both Herschels, William in England and John in South Africa, discovered regions of diminished stellar population, and even a few utterly blank spots devoid of any perceptible light. Caroline Herschel recalled that when her brother swept his 48-inch reflector from Ophiuchus into Scorpius, he cried out (in German, his native tongue), "Here is surely a hole in heaven!" To his utter amazement, a field near Rho Ophiuchi was bereft of even the faintest star image.

Herschel had previously rejected a theory that globular clusters were, in effect, glimpses of rich star fields popping into view through 'tunnels' leading outwards, through an obscuring medium. Because of the unlikelihood of finding such a multiplicity of bright holes all pointed straight at the earth, Herschel was troubled that his dark holes were also a flawed conception, but observational astronomy could offer no better explanation.

According to a paper by Dr. Elizabeth Lada, professor of astronomy at the University of Florida, William Herschel "apparently did not attach too much greater significance to this... However, [his sister] Caroline appears to have guessed that this... held a potentially greater significance." A half-century later, using observations made in South Africa by her nephew John and the large body of her brother William's data, gathered with her assistance, Caroline Herschel compiled the first catalog of dark nebulae (containing 33 entries, cited in a 2006 article by Dr. Michael Hoskin of Cambridge University, a scholar of Caroline Herschel's scientific work.) Dr. Lada states that "It wasn't until the early twentieth century that the work of Barnard and Wolf conclusively demonstrated that these startling vacancies in the sky were true astronomical objects-- dark obscuring nebulae and it took another half century until astronomers proved them to be the birth sites of all stars and planets in the galaxy, amply confirming Caroline's intuition concerning their importance in the pantheon of astronomical objects." [update from recent research, added 7/07]

William Herschel did not specifically describe the Horsehead nebula (and indeed it may be necessary to have prior experience with a photograph of the object to perceive its subtle contrast visually in the telescope eyepiece), though he did record the area around the star Zeta Orionis in Orion's belt (his region No. 25) as exhibiting much "diffused milky nebulosity'' that today is visible even through binoculars in a sky with little light pollution and no moonlight.

To discern such faint and elusive phenomena, Herschel donned a black hood while standing at the mouth of his telescope, viewing the light directly reflected from the large mirror into his home-made eyepiece without the loss of a secondary reflection by means of prism or diagonal mirror. If Herschel's efficiency calculations were accurate, his large spectrum, untarnished, was capable of the visual performance of a modern 42-inch aperture aluminized mirror. There is little wonder that Herschel could see objects that went undetected in the smaller long focal-length refractors of 19th century observatories.

THE PIONEERING PICKERINGS

In his early days, William believed that the future of astronomy lay in the promise of photography, and helped persuade elder brother Edward to establish a program at the Observatory, under the younger Pickering's direction, that would eventually lead to the nearly 500,000 invaluable plates in the Harvard collection. An elaborate report published by William Pickering in 1895 summarized his early photographic explorations of the Moon, planets, and especially the great nebula in Orion.

William's team included A. E. Douglass, his later collaborator at Lowell Observatory, and the legendary photographic technician E. S. King. Together they determined the effectiveness of using a very short focal-ratio in capturing the fastest possible exposures of faint stars and nebulousity; the requirements for accurate tracking clocks and guiding procedures; the techniques of developing, enlarging, enhancing, and printing their images with best contrast; and standardizing exposures for long-term comparative studies. Improvements were made to pre-electric photometric light sources, and a study of sky-fogging due primarily to gaslight yielded important information in the "time corrections" of plates, in essence controlling long-term reciprocity failure, the discovery of which is usually credited to others than Pickering's group.

Though early Harvard test photographs of the Zeta Orionis nebulosity were distributed at the Paris Astrophotographical Congress in 1887, it was an especially good plate of the belt region of the constellation of Orion, Harvard No. B2312, that would be publicized as the Horsehead discovery plate. The exposure was made by Pickering and his team on February 8, 1888, and it, along with numerous other plates collected over the past months, were turned over to the Harvard College Observatory "computing" staff, headed by one of the most important (though unlikely) early women figures in astronomy, Mrs. Williamina Paton Fleming (1857-1911).

Williamina P. Fleming, courtesy of Harvard College Observatory Archives

Arriving in Massachusetts from her native Scotland in 1878, Mrs. Fleming went to work in the household of E. C. Pickering -- as his second maid! Impressed with her personality, accuracy, and persistence, Pickering hired her to help part-time at the Observatory, and ten years later she was now an indispensible staff member (despite her lack of specific college-level astronomical or science training) who had become the head of the women performing the tedious long-hand mathematical computations.

Because of her exceptional competence, Mrs. Fleming was given the task of examining the plates to measure positions and note discoveries of nebulae.

On June 27, 1888, she recorded the large area of nebulosity extending south of Zeta Orionis for about 60 minutes of arc, containing: "a semicircular indentation 5 minutes in diameter 30 minutes south of Zeta. All good plates of this region show this object, and it has been used here as a test for some time", states the Harvard College Observatory Annal for 1890.

The official published table of new nebulae found photographically by Harvard thus lists the Horsehead region as having been discovered by W. P. Fleming. So far, so good: but did the original plate still exist?

The image shown here is derived from the discovery plate: a large-scale 8x10 photographic print of Orion's belt stars, which we have cropped and magnified, centering on the region around Alnitak. In order to produce a usable image for ASTRONOMY in 1990, it was converted to a half-tone by the photographic lab at Lick Observatory. Our only extant example is a photocopy, which has been scanned and enhanced: the contrast is much greater than on the print of the original plate, to show every possible amount of the bright and dark nebulosity thereon.

Because few in the astronomical world were at that time interested in obscure faint nebulae, W. H. Pickering is far more renowned for his discovery in 1899 of Saturn's ninth moon Phoebe, and Mrs. Fleming is recalled for her work in classifying stellar spectra. Another achievement slipped through William Pickering's fingers: the discovery of Pluto. Despite Pickering's work for over 15 years in refining an orbit for a proposed trans-Neptunian planet (using a graphical method of curve-fitting found to be crude and fatally flawed by Philip M. Sadler of the Harvard-Smithsonian Center for Astrophysics), and his achievement of closely predicting the actual position of the planet, the credit for Pluto rightfully belongs to Clyde Tombaugh and the Lowell Observatory.

William Pickering and Williamina Fleming probably failed to achieve their due credit for the discovery of the Horsehead because of the listing in the "Index Catalog" supplement to the New General Catalog of Dr. J. L. E. Dreyer. The nebular region south of Zeta Orionis -- No. 434 in Harvard's published list of new nebulae -- was printed by Dreyer in 1895 with the designation IC-434, the discoverer of that and all relevant others listed simply as "Pickering" (a reference that is associated in the original catalogue with the full name of the Director of Harvard College Observatory, E. C. Pickering): thus, we may perhaps understand the confusion of later references which may overlook W. H. Pickering's closer involvement in the immediate work leading to the discovery.

Whether Dr. Dreyer had chosen not to publish Harvard's attribution of the discovery to Mrs. Fleming may be because he felt -- as a leading European professional astronomer and academic himself -- that her superior, the Observatory director, deserved the credit instead of his humble underling. Or indeed it may be because of the wide-spread male chauvinism of the period before women's suffrage. According to Steven H. Yaskell's article, "Henrietta Swann Leavitt, the star catcher" in the Autumn 2005 issue of the The Northern Astronomical Review, E. C. Pickering was, for his time, a feminist who bucked the current attitude that regarded women as intellectually inferior, suited only to mundane manual labor. Though he could be patronizing, Pickering nonetheless gave remarkable support to the rights of his "women computers" and often took their side in disputes with male Observatory staff. Thus, there is no surprise that he gave full academic credit to the work of Henrietta Leavitt, Annie J. Cannon, and Wilhelmina Fleming for their scientific contributions to Harvard's astronomical research.

Update, 3/07:  Click here for our companion article about another object discovered by Mrs. Fleming, IC-420, showing the original IC page that attributes these discoveries of hers from 1888 to "Pickering", as well as links to Harvard publications that properly identify the discoveries as being hers.

THE KINDRED SPIRITS OF THE NEBULAE

Dr. Max Wolf, from the private collection of Prof. E. S. Holden, courtesy of the Mary Lea Shane Archives of Lick Observatory

Max Wolf, unlike the impoverished youth Barnard, was the son of a wealthy physician and obtained a superb scientific education in one of the greatest university centers in Germany. Eventually heading the Heidelberg Observatory, Dr. Wolf soon discovered that short focal-length telescopes were necessary for effective photographs of both dim stars and faint spread-out nebulously, a fact then appreciated by few.

Wolf first photographed the region of Zeta Orionis with a 5.25-inch aperture "Kranz-Euryscope" at Heidelberg on the night of January 2, 1891. The exposure time was 5-1/2 hours, a task which Wolf found so daunting that he required two assistants; Barnard would take such exposures in stride all by himself.

Max Wolf quickly sent out word of what he believed to be his own discovery, submitting his picture of the "marvelous object" around Zeta Orionis to the British Astronomical Association Journal, which published a crude early half-tone reproduction "with an unimportant re-touch". But editor E. Walter Maunder noted that the object was obviously the same phenomenon earlier photographed by W. H. Pickering of Harvard College Observatory.

The image shown was taken from a very dim, primitive early half-tone with almost no gray-scale, found in the Lick historic collection copy of the British Astronomical Association journal from 1891. Some reprocessing to stretch contrast was done by the photo lab at Lick Observatory, but -- unfortunately -- that copy has been lost by Kalmbach.

Thus, the picture was further degraded by our surviving photocopy, and required extensive digital image processing to improve the distinction; though IC-434 and the Horsehead region are recognizable, the result is unnatural compared to what one would expect from Wolf's original negative.

Edward Emerson Barnard -- whose life and work on dark nebulae has been recounted in Gerrit Verschuur's fascinating book Interstellar Matters, as well as in his February 1989 ASTRONOMY Magazine article ''Barnard's Dark Dilemma" -- photographed the Horsehead at Lick Observatory on Mt. Hamilton on the night of October 3, 1894.

Edward Barnard, obscured by controls of the Crocker Telescope with the Willard Lens, Mt. Hamilton, courtesy of the Mary Lea Shane Archives of Lick Observatory

Barnard had suffered a poverty-stricken, fatherless childhood during the depths of the Civil War, and had performed the Herculean task of raising himself up from a state of unschooled ignorance to acquiring notoriety as a discoverer of comets. After struggling hard to obtain a college degree at Vanderbilt University, Barnard at last achieved his dream of being an astronomer, becoming a staff member at the new Lick Observatory, whose imperious Director Edward S. Holden at first seemed to be a father figure to be revered.

Holden had acquired an old, obsolete wet-plate-era camera portrait lens that had been used with success in an 1889 eclipse expedition by an amateur photographer. The lens had been made in 1849 in New York City, and had been sold by a dealer named Willard. Since it was no longer necessary to use camera apertures of 5 or 6 inches for the new and more sensitive dry places for commercial photography, these old portrait lenses could be purchased for a fraction of their original cost.

Barnard made some test exposures of the Milky Way region with the Willard lens in 1889, and the results were so encouraging that Holden sent the lens to the esteemed instrument maker John A. Brashear for re-figuring. By 1892, Edward Barnard embarked on a long program of obtaining the first complete photographic catalog of the glories of the Milky Way, but was not to be able to publish his superb Willard lens plates until 1913 due to his disputes with Holden (whom he later had come to despise and distrust), Barnard's incessant striving for perfection in reproducing the originals, and his difficulty in securing funds to cover the publication costs.

By the time of the printing of the early Willard plates, Barnard had been on staff at Yerkes Observatory at Williams Bay in Wisconsin for nearly two decades, and had already taken much better and deeper exposures of the Milky Way with Catherine Bruce's 10-inch telescope. Yet the early Willard plates were of such interest that they were revelations to most astronomers at the time of their publication, and are very fine even today.

The Horsehead image is not as firmly registered as in the Harvard photograph made at a narrower scale and slightly higher magnification, but it is clearly discernible on a comparable later original Willard camera glass plate, as I found when examining the precious objects in the Lick Observatory plate vault under the supervision of long-time Lick photographic investigator Eugene Harland, who takes care of the historic observing books and plates of the century-old University of California observatory.

In Barnard's image, above, the lengthy exposure -- to show the faintest nebulosity that his equipment could register at the time -- caused the Great Orion Nebula (M-42) to be "burned in". He had to stop down the edges of the Willard Lens to improve the definition of star images at the edges of the field of his huge plates, so his effective focal ratio was probably higher than optimal just for recording nebulosity. Truly, his Milky Way pictures taken with the Willard Lens were not merely produced to provide only scientific data, but also were "beautiful pictures" that showed Barnard's immense skill and sense of aesthetics.

A computer enhancement of the region of Zeta Orionis, converted to a negative and employing heavy processing to average the noise levels and stretch the contrast range, reveals that the Horsehead region was well registered, preserved even on the photocopy we possess of the exquisite collotype print of the 1894 Milky Way plate in the Lick Observatory publication. It was, in fact, more evident to our eye -- the last time we saw the magnificent folio in person years ago -- than it is in this interpretation.

My colleagues in this project, Richard Page (an amateur telescope-maker and observer who has helped confirm a comet discovery by Donald Machholz) and the astrophotography team of Ron Wood and his son Ryan posed with the Willard lens for Gene Harland's photograph in the hallway of the Lick Observatory main building, as shown below.

Willard Lens in 1989: left to right, Rich Page, Steve Waldee, Ron and Ryan Wood.

In the next part of the Horsehead story, Isaac Roberts and Edward Barnard square off on the subject of Herschel's 52 nebular regions, and photography and astronomy advance into the era of Big Science.

Click for Part Two: The Horsehead Takes on Its Shape and Name

Footnote.
¹Even today, in October 2005, the author (Waldee) continues to encounter information about the Horsehead on the Internet that we feel may derive from the early distortion of facts that we uncovered in our research, such as the explanation on the "SEDS" page for the Horsehead, which we copied on 10/20/05 as stating: "E. Pickering detected IC 434 photographically in 1889, the Horsehead can be detected on a photo made on January 25, 1900 by Isaac Roberts (Roberts 1902). E.E. Barnard recognized the object in the 1910s." (See link, which may or may not be revised at a future date.) According to our research, however, these claims about "E." Pickering and Barnard are refuted in the clear public record of the Harvard College Observatory and the professional astronomical journals we investigate in these present articles.

And leading magazine articles, as well as books, are still misrepresenting the history of the object. The author Waldee was dismayed to find that in the otherwise interesting and colorful discussion of the Horsehead nebula in the December 2006 issue of Astronomy magazine (pp. 66-71), the discovery is presented, in this writer's opinion, quite wrong, in the conventional distorted account of resources that fail to rely on the authentic original Harvard documents! E. C. Pickering, not his brother William, is incorrectly credited as the photographer, and no mention is made of the object's actual first discoverer, notator, measurer, and cataloguer: Mrs. Fleming. This is especially frustrating, as this very magazine and its then current editor had in 1990 requested and received the papers researched by Waldee and printed on this website, accurately quoting the original documents. - srw. Return to section.

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