The Role of Images in Astronomical Discovery Read online

  the sole purpose of rapidly photographing the whole sky over periods as short as a month.

  Leading survey telescopes are the Panoramic Survey Telescope and Rapid Response System

  (PanSTARRS) in Maui, Hawai’i and the Large Synoptic Survey Telescope (LSST) in Chile.

  But let us return to the pioneering work of nebular photography of the nineteenth

  century.

  18 D. Sobel, The Glass Universe, How the Ladies of the Harvard Observatory Took the Measure of the Stars, New York: Viking, 2016.

  19 B. M. Lasker, M. G. Lattanzi, B. J. McLean, et al., The Second-Generation Guide Star Catalog: Description and Properties, The Astronomical Journal, 2008, Vol. 136, pp. 735–776. The GSC2.3 catalogue contains the astrometry, photometry, and classification for 945,592,683 objects.

  20 The Sloan Digital Sky Survey, or SDSS, was a photographic and spectroscopic survey conducted with a wide-field 2.5-m telescope in New Mexico, USA.

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  Part I – Images and the Cosmos

  Roberts’ System Engineering Approach

  Because “nebulae” were faint, they proved to be very challenging targets for celestial pho-

  tography. When he retired in 1888 at the age of 59, Isaac Roberts (1829–1904), a wealthy

  Welsh engineer and businessman, decided to devote his time to his passion for science,

  especially astronomy and geology. A dedicated amateur astronomer, and self-educated,

  Isaac Roberts rushed into nebular photography. He pushed astrophotography to new lev-

  els of performance by introducing new observing techniques and modifying the traditional

  telescope set-up, following an observing arrangement favored by a fellow-countryman.

  Isaac Roberts, like Parsons and several others, belonged to an unusual class of individuals

  who conducted independent astronomical research. British geologist and historian Martin J.

  S. Rudwick writes about the awakening of “gentlemanly specialists” in the world of early

  nineteenth-century geology.21 Astronomy, alongside geology, was an area of interest for

  curious minds. For British science historian Allan Chapman, “The independent tradition of

  astronomical research came into being, then, through a combination of intellectual curios-

  ity, independent money, and public-spiritedness, for if you were Irish, Scottish, Welsh or

  English in 1840, and you wanted to attempt to ‘fathom’ the universe, it was no use to get

  into the good books of a king, a publicly funded academic body or an all-powerful minis-

  ter of state in pursuit of patronage . . . ”22 Chapman described these individuals as “grand

  amateurs.”23 And as history showed, grand amateurs, including Parsons, were amazingly

  visionary and turned out to be quite successful. In particular, the Rosse program and its

  engineering approach served as a model for the Grubb–Parsons firm owned and led by

  Thomas and Howard Grubb, the great Victorian telescope makers.24

  Particularly innovative in telescope design was William Lassell (1799–1880), a suc-

  cessful merchant and brewer of Liverpool. As a true grand amateur, Lassell had already

  demonstrated that an equatorial mount, which kept the telescope fixed in declination, with

  one single movement around a polar axis, was to be favored for making continuous obser-

  vations. As a friend of Parsons and a frequent visitor to Birr Castle, Lassel understood the

  limit of the Leviathan mount. Lassel’s equatorial set-up allowed the object being observed

  to be kept in the center of the field of view. It eliminated repeated manual re-centering and

  enabled uninterrupted observations for sketching nebulae or any other objects.25

  Roberts followed in these footsteps. He understood the impact and potential of the long

  exposures that were allowed by dry photographic plates. The new emulsions made it possi-

  ble to reach objects much fainter than anything the eye could see through the telescope. To

  21 M. J. S. Rudwick, The Great Devonian Controversy: The Shaping of Scientific Knowledge among Gentlemanly Specialists, Chicago: University of Chicago Press, 1985.

  22 A. Chapman, William Parsons and the Irish Nineteenth-Century Tradition of Independent Astronomical Research, in William Parsons, 3rd Earl of Rosse: Astronomy and the Castle In Nineteenth-Century Ireland, C. Mollan (editor), Manchester: Manchester University Press, 2014, pp. 271–297.

  23 A. Chapman, The Victorian Amateur Astronomy: Independent Astronomical Research in Britain, Hoboken: Wiley, 1999.

  24 I. S. Glass, Victorian Telescope Makers, The Lives and Letters of Thomas and Howard Grubb, Bristol: Institute of Physics, 1997.

  25 O. W. Nasim, Observing by Hand: Sketching the Nebulae in the Nineteenth Century, Chicago: University of Chicago Press, 2013, p. 190.

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  Fig. 3.1 Isaac Roberts’ 20-inch reflector counter-balanced with the 7-inch Cook refractor. From Isaac

  Roberts (1893), A Selection of Photographs of Stars, Star-Clusters and Nebulae, Courtesy of John G.

  Wolbach Library, Harvard College Observatory. 2016.

  get the full benefits of a long exposure time, Roberts improved telescope systems for accu-

  rate tracking during the several hours required to keep a given object right at the same point

  in the focal plane of the slowly moving telescope. He first adopted the equatorial mount

  design that Lassel had successfully used for operating relatively large reflectors. Roberts

  also introduced another critical but simple innovation.

  If a telescope is being used to photograph, one cannot look into it at the same time.

  Despite good clock drives developed in the last decades of the nineteenth century, no track-

  ing system was precise enough to keep an object perfectly centered over a 90-minute expo-

  sure time; fine adjustments had to be made more or less regularly. Roberts introduced the

  “piggyback” guide scope to follow a reference star; he mounted this second telescope in

  place of the traditional counterweight of equatorial mounts (Fig. 3.1). Using the 7-inch

  Cooke guide refractor on the same mount as the telescope used for the photography, he

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  Part I – Images and the Cosmos

  could keep an appropriately chosen star exactly on the reference crosshair of the eyepiece.

  Manually correcting any slight deviation in the tracking motion of the telescope, it was

  easy to compensate completely and precisely for the rotation of the Earth and for distur-

  bances triggered by wind squalls or hiccups of the telescope clock drive. These adjust-

  ments allowed the observer to keep the camera aimed accurately during exposures lasting

  hours. This was crucially important for deep photography that was capable of capturing

  low-surface-brightness “nebulae.”

  All this required painstaking efforts but led to many fine photographs. After experi-

  menting with the 7-inch imaging refractor, Roberts purchased a 50-cm reflector telescope,

  equipped with a very accurate clock drive, from Irish optical designer Howard Grubb

  (1844–1931). The camera set held 102 × 102 mm silver-on-glass photographic plates that

  allowed a 2 × 2 degree field of view at the celestial equator. The equipment was the heart

  of Roberts’ private Crowborough Observatory in Sussex, England, making his home-based

  facility probably t
he first one fully dedicated to astrophotography. Robert’s set-up was a

  marvel of innovations. His system engineering approach to telescope design and operation

  was a step toward the modern telescope. It was the demonstration of fine work from a true

  grand amateur.

  Saving the Magic Half a Second

  The Birr Castle observers have described eloquently how the sharpness of images seen

  through the telescopes changed under varying atmospheric conditions. Leviathan observer

  George Johnstone Stoney (1826–1911) commented that bright stars “are usually seen

  as balls of light, like small peas, violently boiling in consequence of atmospheric

  disturbance.”26 Astronomers call this boiling “seeing”; it degrades image quality, and is

  one of the reasons for putting telescopes in space. Moments of exquisite atmospheric sta-

  bility, when for a fraction of a second the atmosphere would freeze, were rare and pre-

  cious. These were the magic “half a second” instants that had to be seized when drawing or

  photographing.

  The question in the mind of everyone who had observed through the eyepiece of a large

  telescope was then this: could the judgement of Birr Castle observers glimpsing faint dif-

  fuse blobs have been affected similarly to Worthington’s biased perspective in studying

  splashing liquid drops? Were the details of “nebulae” seen and drawn as observed through

  the powerful 3-ft and 6-ft telescopes, but through the “boiling” atmosphere, just the “fancy

  of the observer” as Wilhelm Tempel claimed. Obviously bothered, Tempel had written most

  critically about the performance of the Leviathan, on the basis that he could not see in his

  11-inch refractor the details of the “nebulae” drawn by the observers of the Leviathan. The

  glaring divergence between drawings of the same object particularly distressed Tempel and

  26 G. Johnstone Stoney, in Fourth Earl of Rosse, Observations of Nebulae and Clusters of Stars Made with the Six-Foot and the Three-Foot Reflectors at Birr Castle from the Year 1848 up to the Year 1878, Scientific Transactions of the Royal Dublin Society, 1878, Vol. II, p. iv.

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  reinforced his skepticism till the end. Joining the skeptical chorus, English science popu-

  larizer Richard Proctor (1837–1888) expressed very strong criticism about the Leviathan

  image quality and performance in the Frazer’s Magazine of December 1869, and spread

  false rumors.27 The patient and meticulous work of the Birr Castle observers was on the

  chopping board and the prognosis was quite bleak.

  The Andromeda “Nebula”: A Masterpiece Image

  Isaac Roberts’ photographs held the answers. Roberts had started photographing Messier

  31, the “great nebula” in Andromeda, in the fall of 1888. Briefly commenting that the “neb-

  ula” “is now for the first time seen in an intelligent form,” he was quickly dragged into a

  speculative discussion about the possibility of this being a new solar system that was in

  the process of condensing from a nebula with a central sun now seen in the midst of nebu-

  lous matter.28 Roberts went back to the “great nebula” and his masterpiece was his 4-hour

  photograph of Messier 31 taken during the night of 29 December 1888 (Fig. 3.2).29 The

  result must have been a relief to many: the beautiful photographic image showed a spiral

  structure, which was conspicuous despite the fact that the plane of the galaxy is tilted signif-

  icantly into the line of sight. The very short paragraph in the article where Roberts reported

  his photographic results on the “nebula in Andromeda” is almost an anti-climax.30 Roberts

  was actually much more voluble in his description of the photograph of the Pleiades. In

  March and April of 1889, 44 years after Parsons’ seminal discovery of spirality, Roberts

  photographed Messier 51, the Whirlpool Galaxy. The image displayed magnificent spiral

  arms.31

  Spirality had been found in several other “nebulae” by Birr Castle observers. Roberts

  now had the technique to freeze spirality on photographic plates, a much more neutral

  medium than drawing from visual observations through variable atmospheric conditions.

  Contrary to Worthington’s frustrating results, photographs of “nebulae” confirmed the spi-

  rality of most of the objects which the Birr Castle team claimed to have identified intriguing

  patterns for. Photographs actually reinforced the regularity and symmetry of many features

  captured and sketched by visual observers.

  The confident Roberts made regular presentations of his photographs at the meetings

  of the Royal Astronomical Society. Less restrained than Parsons in commenting on the

  nature of “nebulae,” Roberts went astray in the physical interpretation of what he had pho-

  tographed. He explained spiral structure as a pattern that could be the resulting material

  from a collision between two stars, or two “nebulae” of counter-moving streams of meteoric

  27 R. A. Proctor, The Rosse Telescope Set to New Work, Frazer’s Magazine for Town and Country, 1869, Vol. LXXX, pp. 754–

  760.

  28 I. Roberts, Photographs of the Nebulae M31, h44, and h51 Andromedae, and M27 Vulpeculae, Monthly Notices of the Royal Astronomical Society, 1888, Vol. 49, p. 65.

  29 Roberts also used a 5 inch Cooke portrait lens that covered over 10 x 10 degrees and produced some stunning photographs.

  30 I. Roberts, Photographs of the Nebulae in the Pleiades and in Andromeda, Monthly Notices of the Royal Astronomical Society, 1889, Vol. 49, p. 121.

  31 I. Roberts, A Selection of Photographs of Stars, Star-clusters and Nebulae, London: Universal Press, 1893, Vol. 1, Plate 30, pp. 85–86.

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  Part I – Images and the Cosmos

  Fig. 3.2 Transformational Image: The First Known Photograph of a Galaxy – Messier 31 –

  Showing the Structure of the “Great Nebula” in Andromeda. It was obtained by Isaac Roberts on

  December 29, 1888. From Isaac Roberts (1893), A Selection of Photographs of Stars, Star-clusters

  and Nebulae. Courtesy of John G. Wolbach Library, Harvard College Observatory.

  material! Certainly inspired by the works of William Herschel and Pierre Simon Laplace,

  he later surmised boldly that the Andromeda “nebula” was a stellar system in formation.

  Clearly the Nebular Hypothesis had become a blinding mantra.

  Roberts’ passion for astrophotography was the fortunate cause of his meeting with a

  sister soul, the young American astronomer Dorothea Klumpke (1861–1942), who would

  play a unique legacy role in highlighting his pioneering astrophotographic work. In 1901,

  Roberts married Dorothea, who was 32 years his junior. Klumpke had obtained a doctorate

  degree in mathematics from La Sorbonne, Paris. When she met Roberts, she was Director

  of the Bureau of Measurements at the Paris Observatory and was in charge of the Carte

  du ciel, which was led by Paris Observatory Director, Admiral Mouchez. Klumpke and

  Roberts had met in 1896 while sailing to Norway with a group of astronomers, to observe

  a solar eclipse.

  Once married, Dorothea left her position to work with Roberts. After Roberts’ death

  in 1904, she completed his astrophotographic project by assembling the collection of

 
photographic plates he had obtained at Crowborough. She published several papers as

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  Mrs. Roberts. In 1929, she released a comprehensive catalogue, The Isaac Roberts Atlas

  of 52 Regions, a Guide to William Herschel’s Fields of Nebulosity, to help observers study

  extensive diffuse nebulosity.32 It was an extraordinarily careful production; the photograph

  of the Messier 31 field is spectacular. In 1934, Dorothea received a crowning honor for her

  career. She was elected Chevalier de la Légion d’Honneur, and received the Cross of the

  Legion from the President of the Republic of France. Klumpke left several gifts of money

  to establish prizes in astronomy and mathematics.

  There is one last consideration when regarding Roberts’ work. His contributions are

  lesser known than those of Parsons. Perhaps Roberts’ rush to interpret the “nebulae” as

  examples or confirmation of the Nebular Hypothesis made him a victim of whiggish his-

  toriography, where losers are forgotten and winners venerated.33 By comparison, Parsons

  emphasized the power of his instruments and the quality of their images, and remained

  extremely cautious in his interpretation.

  Unsettling “Grand Amateurs”

  From William Herschel all the way to William Parsons, it can be seen that it was those indi-

  viduals with mechanical genius and a knack for solid management who made and improved

  large reflectors and used them in creative ways. It seems remarkable that businessmen were

  able to move into the world of astronomy late in their life. Parsons made significant con-

  tributions not only in building the largest telescopes of the nineteenth century, but also in

  developing new and systematic approaches to astronomical observing and telescope opera-

  tions. Also striking were the groundbreaking contributions of these individuals who trans-

  formed themselves into devoted astronomy grand amateurs and who audaciously pushed

  the technology of large reflectors and the use of astrophotography. They all shared a strong

  interest in “nebulae,” which drove their technical innovation. Like Allan Chapman, Alan