The Role of Images in Astronomical Discovery Read online

  As finely described and analyzed by Harvard University historian Peter Galison, scien-

  tists have been very creative at developing and using a whole arsenal of machines. In his

  monumental Image and Logic, Galison contrasts the visual and logical approaches of the

  scientific method. One tradition aims at producing “images of such clarity that a single pic-

  ture can serve as evidence for a new entity or effect.”19 Against imaging, Galison contrasts

  the “logic tradition” where electronic devices, amassing signals, act as counting machines

  instead of picturing machines. In all fields of science, quantitative measurements are an

  essential basis for assembling factual data in order to identify processes, reconstruct behav-

  iors and establish trends. The two approaches complement each other.

  In the battery of tools for observing and measuring, images and the ways to record

  them are outstanding. “Part of the déformation professionnelle of scientific observers is a

  16 L. Daston and P. Galison, Objectivity, New York: Zone Books, 2007, p. 367.

  17 L. Daston and E. Lunbeck (editors), Histories of Scientific Observation, Chicago: University of Chicago Press, 2011.

  18 L. Daston, The Empire of Observation, 1600–1800, in Histories of Scientific Observation, L. Daston and E. Lunbeck (editors), Chicago: University of Chicago Press, 2011, p. 85.

  19 P. Galison, Image and Logic: A Material Culture of Microphysics, Chicago: University of Chicago Press, 1997, p. 19.

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  Introduction

  Fig. 0.3 Orion Nebula photographed with the 36-inch telescope by Andrew Common in 1883. Credit:

  Institute of Astronomy, University of Cambridge.

  near-obsessive preoccupation with their objects of inquiry.”20 What is captured in an image

  can often be measured and put into graphic forms, or non-representational pictures, to sum-

  marize and convey information as effectively as possible (Chapter 4).21 Commenting on

  Ernst Haeckel’s experience of nature, Olaf Breidbach writes, “The very act of looking at

  nature was the best way of understanding it. Illustrations were not simply images of nature –

  they were the very embodiments of scientific knowledge. And a scientist was someone who

  illustrated his observations of nature in such a way as they could be shared by those not in

  a position to carry out discoveries for themselves.”22 The illustrations become scientific

  working objects.

  “Working objects can be atlas images, type specimens, or laboratory processes – any

  manageable, communal representative of the sector of nature under investigation. No sci-

  ence can do without standardized working objects, for unrefined natural objects are too

  quickly particular to cooperate in generalizations and comparisons.”23 In astronomy, exam-

  ples of working objects are archetypal objects such as the Orion Nebula (Fig. 0.3), the “great

  galaxy” in Andromeda (Fig. 0.4, Plate 1.1), the Omega Centauri globular cluster (Fig 0.5),

  20 L. Daston, On Scientific Observation, ISIS, March 2008, Vol. 99, No. 1, pp. 97–110, p. 107.

  21 E. R. Tufte, The Visual Display of Quantitative Information, Cheshire CT: Graphics Press, 1983.

  22 O. Breidbach, Visions of Nature, The Art and Science of Ernst Haeckel, Munich: Prestel, 2006, p. 20.

  23 L. Daston and P. Galison, Objectivity, New York: Zone Books, 2007, p. 19.

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  Introduction

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  Fig. 0.4 Messier 31, the Andromeda Galaxy, imaged with the Spitzer Infrared Space Telescope.

  The image shows the galaxy at a wavelength of 24 microns in the mid-infrared. Credit: NASA/JPL-

  Caltech/Karl Gordon.

  Fig. 0.5 Center of globular cluster Omega Centauri. The cluster is about the size of the full Moon in

  apparent size. Credit: ESO.

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  Introduction

  Fig. 0.6 Two pages of the NASA Atlas of Galaxies by Sandage and Bedke (1988). Courtesy of NASA

  Scientific and Technical Information Division.

  the Sun and several other objects of the northern and southern celestial hemispheres. Image

  compendia, in particular atlases of galaxies, are other forms of working objects (Fig. 0.6).

  Non-representative images can also be working objects. Hertzsprung–Russell diagrams,

  which distribute stars of different luminosities as a function of their colours, have been

  powerful working objects to help understand the evolution of stars. Comparable diagrams

  have been created to describe and separate classes of galaxies. Working objects are the

  material from which concepts are developed and applied to broader classes of objects.

  Images at Work

  The image tradition is the center of our attention. Several groundbreaking images helped to

  unravel the world of galaxies, showing evidence for a new entity or effect. As a conducting

  thread of the book, I will present several noteworthy images. Transformational images, like

  Lord Rosse’s first drawing of Messier 51, or the photographic plates obtained by Edwin

  Hubble identifying variable stars in the Great Andromeda Nebula, are not necessarily spec-

  tacular from an “aesthetic” viewpoint. Actually they are often quite bland to the unfamiliar

  eye. Furthermore, what appears on an image may not be at all obvious; instead it may act as

  evidence for something thus far unknown or poorly understood, for example the map of the

  distribution of galaxies in the Coma cluster and Virgo cluster of galaxies, first by William

  Herschel in 1785, then by Fritz Zwicky 150 years later. Only a trained eye will notice the

  unusual concentration and relative symmetry of these systems of galaxies.

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  Introduction

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  Fig. 0.7 X-ray diffraction image, Photo 51, of DNA taken by Raymond Gosling in May 1952. Gosling

  was working under Rosalind Franklin on the structure of DNA. Credit: King’s College London.

  To wrap up this introduction, I present three examples taken from molecular biology and

  astronomy and show how the “visual approach” helped cut through new frontiers. These

  examples illustrate different aspects of the cognitive challenges which images can present

  to the inquisitive scientist; in particular, that images are not self-evident.

  The discovery of the molecule deoxyribonucleic acid (DNA) and its role in carrying

  genetic instructions in the reproduction and growth of living organisms is considered a

  momentous event of twentieth-century science. In the early 1950s, English chemist and

  crystallographer Rosalind Franklin (1920–1958) produced critical X-ray diffraction images

  of DNA, which rapidly led to the identification of the double helix structure of the molecule

  by James Watson, Francis Crick and Maurice Wilkins in 1953. One historical image is

  Photo 51 (Fig. 0.7). It is not a direct image of an object; Photo 51 shows the microscopic

  diffraction pattern produced by structures at the molecular level by shining X-rays on them.

  To get the shape of the real thing, i.e. the double helix, one needs to do a mathematical

  transformation of the diffraction pattern. Photo 51 was crucial to Crick and Watson for

  their derivation of the tilt of the helix, i.e. the angle from the perpendicular to the long axis,

>   the distance between the chemical bases, and the length of a full turn of the helix. The

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  Introduction

  Fig. 0.8 Sunspots drawn by Galileo on 23 June, 1612. From Istoria e Dimostrazioni Intorno alle

  Macchie Solarie e Loro Accidenti. Courtesy of The Elliott and Eileen Hinkes Collection of Scientific

  Discovery, The Sheridan Libraries, Johns Hopkins University.

  cognizant steps between seeing Photo 51 and reaching the groundbreaking conclusion of

  the DNA helix structure took only a few months. However, the translation of Photo 51 into

  modern colour-coded representations of the DNA two-base pairs is undecipherable to the

  unfamiliar onlooker.

  The second example calls for a more recognizable cognitive operation in analyzing what

  is seen, but where the correct understanding of the phenomenon required centuries of inves-

  tigation, with lots of speculation. Sunspots were drawn with great accuracy as soon as tele-

  scopic solar observations could be conducted in the second decade of the seventeenth cen-

  tury (Fig. 0.8). Early visual observations and drawings of sunspots drove Galileo Galilei

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  Introduction

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  Fig. 0.9 Green pea galaxy J0925+1403 imaged with the Hubble Space Telescope. Credit:

  NASA, ESA.

  (1564–1642) and Christopher Scheiner (1573–1650) to claim that the solar surface was not

  “pure and featureless.” Sunspots apparently moving on the solar surface showed instead

  that the Sun was rotating on itself. Nevertheless, it took until the beginning of the twentieth

  century to explain the somber regions on the Sun not as volcanoes but as localized regions

  of strong magnetic fields. For almost three centuries, solar astronomers kept making superb

  sketches of sunspots without having a clue of what they were or what was causing them.

  Finally, the recent case of the Pea Galaxy, Hanny’s Voorwerp, illustrates the serendipi-

  tous power of studying images through simple visual examination. Engaged in the Galaxy

  Zoo project to classify a large number of galaxies from the Sloan Digital Sky Survey,

  the young Dutch “zooite” Hanny van Arkel came across a few small, in apparent size,

  weird-shaped objects (Fig. 0.9). The objects ( Voorwerp in Dutch) came out with the domi-

  nant colour green because of strong spectral emission in the doubly ionized oxygen line at

  500.7 nm due to intense star formation, hence their name. The unusual object became the

  archetype of a new class of galaxy. In this case, an astute non-professional observer was

  capable of extracting useful astrophysical information from a maze of images.

  These examples show how diverse the paths from imaging to knowledge and under-

  standing can be. In the coming chapters, we will explore the tortuous history of viewing

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  Introduction

  “nebulae,” imagining these foamy celestial entities and finally understanding galaxies.

  Instead of the few months between Photo 51 of DNA and the derivation of its double helix

  structure, this journey took one thousand years.

  The production and use of images, as well as the fumbling with wildly diverse inter-

  pretations, are not unique to astronomy. Images have been engines of scientific exploration

  and discovery in many disciplines as varied as subatomic physics, geology, botany, biol-

  ogy and neurology. Even in mathematics, image representation is a very powerful revealer

  as illustrated by the vivid and spectacular Mandelbrot sets to represent fractal geometry.

  I will use several disciplinary examples, and I will reflect on how astronomy shares with

  other disciplines the discovery power of images, reminding us that there are very close links

  between the images, the apparatus used to obtain or reproduce them and the technologies

  of the time. For example, highlighting the importance of the means of reproduction for

  visual communication, Martin Rudwick has shown how the new techniques of aquatint,

  wood/steel/copper engraving and lithography made reliable reproductions possible in the

  1830s and transformed geological illustrations in publications.24

  24 M. J. S. Rudwick, The emergence of a visual language for geological science 1740–1840, History of Science, 1976, Vol. XIV, p. 151.

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  Part I

  Images and the Cosmos

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  Viewing Heavenly Mist

  Learning to see was never, is never, will never prove effortless.

  Lorraine Daston and Peter Galison 1

  Of the four thousand nebulae which have been recognized, that [Great

  Andromeda Nebula] which forms the subject of the present account is the

  only one the discovery of which preceded the invention of the telescope.

  George P. Bond 2

  Can Galaxies Be Seen with the Naked Eye?

  Caroline Herschel (1750–1848) is probably the most famous woman in the history of

  astronomy (Fig. 1.1).3 Caroline, whom Astronomer Royal Nevil Maskelyne (1732–1811)

  addressed as “Dear Sister Astronomer,” was indeed an outstanding woman. She was only

  1.3 meters (4 ft 3 inch) tall having been struck with typhus that stopped her physical growth

  at the age of ten. Her physical handicap did not prevent her from becoming a fine soprano

  singer of Handel’s oratorios, and later, an active astronomer as she embarked on the auda-

  cious ventures of her older brother William. A musician and a composer, William Her-

  schel had moved from Hanover, Germany, to England for better opportunities in musical

  performance.4 Initially venturing into astronomy as a sideline occupation, William rapidly

  became passionate, even obsessed, about astronomical observing and telescope making.

  Alexander, a younger brother, was also involved in the work of the siblings.5

  Caroline became a skillful astronomical observer, discovering eight comets. She was

  outstandingly competent, highly supportive of her older brother and had her own inter-

  ests in astronomy. Around year 1780, she surmised that “nebulae” were not scarce and that

  these objects were scattered over the whole sky. She and her brother observed and compiled

  “nebulae” for decades. After William’s death in 1822, Caroline returned to Hanover where

  1 L. Daston and P. Galison, Objectivity, New York: Zone Books, 2007, p. 161.

  2 G. P. Bond, An account of the nebula in Andromeda, Memoirs of the American Academy of Arts and Sciences, New Series, 1848, Vol. 3, pp. 75–86.

  3 For a fine overview of the career and contributions of Caroline Herschel, see M. Hoskin, Caroline Herschel as observer, Journal for the History of Astronomy, 2005, Vol. XXXVI, pp. 373–404.

  4 W. Herschel, Symphonies, London Mozart Players, Matthias Bamert, Colchester: Chandos Record Ltd.

  5 M. Hoskin, Discoverers of the Universe: William and Caroline Herschel, Princeton: Princeton University Press, 2011, pp. 23–24.

  17

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  Part I – Images and the Cosmos

  Fig 1.1 Caroline Herschel. Credit: University of Cambridge, Institute of Astronomy.

 
she completed a catalogue of close to 2,500 star clusters and “nebulae.” She was awarded

  the 1828 Gold Medal of the Astronomical Society of London (later Royal Astronomical

  Society) for the catalogue. British astronomy historian Michael Hoskin has written in detail

  about the work of the Herschels.6 He has emphasized appropriately the contributions of Car-

  oline and her recognition that the sky was literally peppered with nebulae: “ . . . her demon-

  stration to William that nebulae were there in abundance awaiting discovery was to prove

  momentous.”7 It was the spark of a grand celestial survey.

  It might be challenging for us more than 230 years later to imagine how critical and

  upwelling was Caroline Herschel’s cosmic uncovering. Anyone who has had the chance to

  look at a nebula or a galaxy through a small telescope will wonder how ancient observers

  managed to figure out these strange sidereal objects. Indeed, nebulae and galaxies observed

  through the eyepiece of rudimentary telescopes remain flimsy and difficult to view; it

  requires effort and lot of patience. Even a modern-day observer, such as Allan Sandage,

  could find observing work miserable and difficult at times. Today, remote-controlled

  6 M. Hoskin, Discoverers of the Universe: William and Caroline Herschel, Princeton: Princeton University Press, 2011.

  7 M. Hoskin, Caroline Herschel as observer, Journal for the History of Astronomy, 2005, Vol. XXXVI, p. 394.

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  1. Viewing Heavenly Mist

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  telescopes with their multiple viewing monitors and comfortable observing rooms have

  made the nighttime work easy and convivial. It is difficult to realize that, up to quite recent

  times, observing was a tough nighttime job tailored for incredibly dedicated individuals.

  Pushing the limits of their tools and managing harsh observing conditions, the Herschels

  came up with impressive insights on the nature of our universe.8 They accelerated the his-

  tory of astronomy on several fronts, in particular in exploring and describing the world of