Among his many contributions to astronomy, Edward E. Barnard’s photographic studies of the galactic plane were the most transformative and enduring. The images themselves, posthumously compiled in A Photographic Atlas of Selected Regions of the Milky Way, remain stunning today. Aesthetically, at least, they hold their own against contemporary multi-color CCD mosaics of star forming regions. They are all the more impressive if we imagine the impact they had on the scientific community in the early 1900s. At that time, our awareness of the luminous structure of the galactic plane was severely limited by the weak sensitivity of the human eye to these diffuse patterns.
Above are a few snapshots I took of the copy of the atlas on the shelves of Princeton’s science library (not an original edition but a reproduction by Cambridge press). I was particularly drawn to the plate centered on rho Oph. Of this field, Barnard wrote,
The region of Rho Ophiuchi is one of the most extraordinary in the sky. The nebula itself is a beautiful object. With its outlying connections and the dark spot in which it is placed and the vacant lanes running to the east from it, it makes a picture almost unequaled in interest in the entire heavens.
Ironically, despite having access to the largest and most advanced observatories of his era, it was a 1.5-inch lens scavenged from a “magic lantern” that led to a major breakthrough in capturing the vast structures strewn along the Milky Way. A magic lantern was an oil-fueled slide projector, a common tool for popular amusement in the decades preceding the cinema. Vistas of emission nebulae and dark lanes, invisible through the 36-inch Lick refractor, illuminated the dry plates at the short focus of the lantern lens. In 1895 he published a description of his apparatus in the second issue of the nascent Astrophysical Journal:
I have elsewhere given some account of the performance of a small lens in photographing large areas of the sky, and for the delineation of very large diffused nebulosities, etc. This lens is a very small one belonging to an ordinary “magic lantern;” it is one and one-half inches in diameter and some four or five inches equivalent focus.
these six photographs with the small lens show us in a most striking manner how the most valuable and important information may be obtained with the simplest means.
In an era when most serious observational work was carried out on long refractors with narrow fields of view, no other astronomer had realized the scientific potential of a low focal ratio objective. Barnard’s engineering efforts in this direction culminated in the construction of the Bruce Telescope, an observatory dedicated to wide-field astrophotography. His wide-field telescopes were true predecessors of many survey-oriented optical observatories in use today, one century on: the Sloan 2.5-meter at Apache Point, the Palomar Transient Factory, Pan-STARRS on Haleakala, VISTA at Paranal, Wide-field Infrared Survey Explorer, etc. In the next decade, LSST and WFIRST will carry that torch.
In 1905, Barnard temporarily relocated the Bruce Telescope from its home at Yerkes Observatory to Mount Wilson in Pasadena. Under the dry Southern California skies he acquired the bulk of the photographs comprising the revered Milky Way atlas. Thanks in large part to these images, the old Herschelian view of the dark nebular features as “vacancies” in the heavens began to be dispelled. Although he was too cautious to entirely dismiss the prevailing theory, he published a classic article in 1919 describing the mounting evidence for the obscuring nature of many of the dark features: http://adsabs.harvard.edu/abs/1919ApJ….49….1B.
The way in which Barnard brought the Milky Way into focus is only one aspect of the man’s life and career I found deeply inspiring to read about. To learn more I recommend William Sheehan’s biography, The Immortal Fire Within.