The Role of Images in Astronomical Discovery Read online

Images of galaxies are at the core of this book (Fig. 0.1, see Plate 6.3). I set the course by

  showing how images have been used for discovery and to further research, with a particu-

  lar emphasis on their link to knowledge and trailblazing roles in the unearthing of natural

  processes.

  Troublesome Images

  Images that we so naturally use as conveyors of information were not always accepted so

  easily. Walking nowadays along the streets and boulevards of bustling Istanbul in modern

  1 A. R. Sandage, Centennial History of the Carnegie Institution of Washington, Volume I: The Mount Wilson Observatory, Cambridge: Cambridge University Press, 2004, p. 195.

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

  3 H. D. Curtis, Modern Theories of the Spiral Nebulae, Journal of the Washington Academy of Sciences, 1919, Vol. 9, p. 217.

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  Introduction

  Fig. 0.1 Hickson compact group 87, about 400 million light-years away in the constellation Capri-

  cornus. The group shows the main morphological types of galaxies: spirals and ellipticals. Viewed

  from the same distance, the Milky Way would look like the tilted spiral at the top of this image. Credit:

  Gemini Observatory.

  Turkey, it is hard to imagine that thirteen centuries ago a battle about images shook the

  ancient city to its societal underpinnings. These were the times of the iconoclasts, those

  who opposed religious images and who destroyed them. Anecdotal history of Byzantium

  reports that the first iconoclast emperor Leo III (c. 685–741) not only closed the imperial

  university, but also had it burnt down along with the library and its professors. Historians

  have shown that the rise to political power of the iconoclast regime and oligarchy in the

  eastern Byzantium Empire during the eighth century triggered a decadent period for Greek

  science. Although the burning story is considered apocryphal, it suggests that the alliance

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  Introduction

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  between images, knowledge and the freedom to search for knowledge have deep roots in

  human intellectual history. “No icons. No Science.”4

  Images of celestial objects are unlikely objects of veneration; making and studying astro-

  nomical images have rarely been controversial. Nevertheless, the association between the

  night sky and images runs deep. For thousands of years, humans have associated the patterns

  of stars in the sky with mythological figures for mnemonics and also for expressing their

  awe at the mysterious celestial vault. “By connecting dots with lines and parts with wholes,

  relations and structures appeared. This marvel had been well known since ancient times, at

  least ever since constellations of bears, angels, heroes, and swans were first marked out in

  the sky.”5 Constellations are images for the mind, and at the same time a tool to assign order

  in the sky while inventing personages or beasts for dreams and imagination. The perpetuity

  of the use of constellations and asterisms, from Antiquity to our times, is a testimony to the

  enduring conceptualizing power of images.

  As in other fields of scientific investigation, astronomical images have generally been

  considered an accepted, and even required, procedure to report on the nature of things. I will

  show that there can be a tortuous path between seeing something and realizing what it really

  is or where it is. Images are a tool of discovery, but are not necessarily self-evident. The sci-

  entific apparatus used to take or reproduce images helps us to see things in new, sometimes

  revolutionary, ways. Scientific images are also an effective means to share information with

  other scientists and the public. This is a theme that has been well studied for other sciences,

  for example in geology by British geologist and historian Martin J. S. Rudwick.6

  Both the discovery process and the sharing are at the root of the creation of the com-

  pendium of images, the scientific atlas.7 In an atlas, pictures are put into a framework. As

  I will demonstrate, the diversity of form and morphology of galaxies allows their images

  to be put side by side in an organized series. As exemplified by the works of German natu-

  ralist Ernst Haeckel (1834–1919), the juxtaposition of images does not necessarily record

  an evolution but a continuity or transition in physical processes or environmental effects.8

  This is a theme that we will come back to in the later parts of the book.

  Let us set the scene by examining the epitome of a discovery image in nineteenth-century

  astronomy.

  Seeing Spirals

  In the late eighteenth century, astronomers William and Caroline Herschel had found “neb-

  ulae” to pepper the sky in almost all directions. German naturalist and explorer Alexander

  4 E. Nicolaidis, Science and Eastern Orthodoxy: From the Greek Fathers to the Age of Globalization, Baltimore: Johns Hopkins University Press, 2011, pp. 40–53.

  5 O. W. Nasim, Observing by Hand: Sketching the Nebulae in the Nineteenth Century, Chicago: University of Chicago Press, 2013, p. 155.

  6 M. J. S. Rudwick, The Emergence of a Visual Language for Geological Science 1740–1840, History of Science, 1976, Vol. XIV, pp. 149–195.

  7 L. Daston and P. Galison, The Image of Objectivity, Representations, No. 40, Special Issue: Seeing Science (Autumn, 1992), University of California Press, pp. 81–128.

  8 O. Breidbach, Visions of Nature, The Art and Science of Ernst Haeckel, Munich: Prestel Publications, 2006, p. 24.

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  Introduction

  von Humboldt (1769–1859) was a visionary scholar. Commenting on the nature of these

  “nebulae,” he boldly coined the expression “island-universes,” a magnificent and visually

  evocative concept.9 In his view, the Milky Way was a giant system of stars that seen from a

  great distance would just appear like one of the many “nebulae” reported by astronomers.

  The concept had already been explored in 1755 by his fellow countryman, philosopher

  Immanuel Kant (1724–1804), who mused over the existence of other universes just like

  our Milky Way (Chapter 5).10 Both men were fantasizing: neither Kant nor von Humboldt

  had any scientific basis for their daring concept. As per Heber Curtis’s quote at the start

  of this introduction, it was a hypothesis explicitly put forward long before it was actually

  substantiated by evidence.

  About a century after Kant proposed his hypothesis, an Irish gentleman was about to

  make a giant leap in probing the “islands” of the cosmic sea. He did it by producing stunning

  hand-drawn portraits of the numerous and then still mysterious foamy patches popping up

  across the whole sky. On a cool and clear night in the spring of 1845, there may have been

  some howling wolves, and certainly some squealing wheels moving the new cantankerous

  machine at Birr Castle, Ireland. William Parsons, the Third Earl of Rosse, was using a

  new giant telescope he had just built and put into operation. Parsons had been observing

  a “nebula” in the constellation of Canes Venatici. The sidereal cloud he was examining

  was already known as listing 51 in the catalogue of French comet chaser Charles Messier.

  Carefully looking through his powerful
instrument, Parsons noticed this time something

  very peculiar: the “nebula” had an overall pattern that appeared like a set of winding arms,

  “an arrangement of curved branches, which cannot well be unreal, or accidental.”11

  Scrutinizing what we now know to be a large galaxy located at about 23 million light-

  years, Parsons had come across a fundamental shape of galaxies. That night he had discov-

  ered a spiral structure (Fig. 0.2). British science historian John North (1934–2008) remarked

  that Parsons “did not fully appreciate what he had found for some time.”12 However, when

  Rosse presented his drawings to the British Association for the Advancement of Science,

  John Herschel made a big deal of them; it must surely have excited the lord. Today, we

  know that spirality betrays a pattern of subtle motions generated by a dynamic instability

  of stars and gas clouds orbiting in the gravitational potential of large disk-shaped galaxies.

  During the following 30 years, William Parsons and Birr Castle’s skillful observers cat-

  alogued thousands of “nebulae.” The drawings of “nebulae” executed by the Parsonstown’s

  observers have made history (Chapter 2). Astrophotography later showed that most of their

  hand-made sketches or portraits were generally correct depictions of the cosmic objects they

  viewed through the eyepiece of the Leviathan (Chapter 3). Yet neither the Earl of Rosse nor

  his observers had even the slightest idea of what these objects really were. They were also

  unaware that, soon following in their footsteps, astronomers would enlarge the size of the

  universe by unimaginable proportions.

  9 A. von Humboldt, Cosmos: A Sketch of the Physical Description of the Universe, New York: Harper & Brothers, 1866.

  10 I. Kant, Universal Natural History and Theory of the Heavens (translated by Ian Johnston), Arlington: Richer Resources Publications, 2008.

  11 C. Parsons (editor), The Scientific Papers of William Parsons, Third Earl of Rosse 1800–1867, London, 1926; Cambridge: Cambridge University Press, 2011, p. 116.

  12 J. North, Cosmos: An Illustrated History of Astronomy and Cosmology, Chicago: University of Chicago Press, 2008, p. 592.

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  Fig. 0.2 Early sketch of spiral “nebula” Messier 51 made by William Parsons in April 1845 (com-

  pare with Fig. 2.10a). The Whirlpool Galaxy is located at about 23 million light-years. Courtesy of

  Wolfgang Steinicke.

  A Rapidly Expanding Universe

  Coming 2,000 years after Greek astronomer Aristarchus of Samos (c. 310–230 BC), Polish

  astronomer and mathematician Nicolaus Copernicus (1473–1543) had blown away the size

  of the Ptolemaic universe by proposing the heliocentric model for the solar system. Coper-

  nicus was attempting to solve the inconsistencies of the Ptolemaic model that had placed

  the Earth at the center of the universe. Instead, Copernicus had the Earth rotating on itself,

  the Moon circling it, and the tandem in revolution around the Sun along with the five other

  visible planets. Like Aristarchus, he positioned the fixed stars as other suns at such great

  distances that they appeared to us as just faint points of light. While the Ptolemaic universe

  had a size 10,000 times the size of the Earth, Copernicus had it at least billions of times

  larger.13

  During the first decades of the twentieth century, our cosmological perspective was

  again dramatically overturned in the wake of the works of several European and American

  astronomers. Unlike Copernicus, these astronomers were not trying to solve tricky celes-

  tial mechanics issues. Working collectively and competitively Heber Curtis (1872–1942),

  Ernst Öpik (1893–1985), Knut Lundmark (1889–1958), Vesto Slipher (1875–1969), Har-

  low Shapley (1885–1972), Edwin Hubble (1889–1953) and Milton Humason (1890–1972)

  13 A. Van Helden, Measuring the Universe, Chicago: University of Chicago Press, 1985, pp. 28–40.

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  Introduction

  were trying to determine the distance to intriguing celestial ‘foamy patches’ (Chapter 5). In

  doing so, they unveiled the world of galaxies in a sequence of stunning observational find-

  ings derived mainly from images obtained with a new generation of powerful telescopes.

  By bringing out the world of galaxies, modern astronomers exploded the volume of the

  Copernican universe by at least 1015 times, or one million billion times. The distances to

  island-universes were found to be colossal, measured in millions, even billions of light-

  years, millions of times further away than any of the stars we see at night. The light-year is

  a commonly used unit of astronomical distance, not of time as its name might suggest. It is

  the distance travelled by light in one year at the velocity of 299,792,458 meters per second;

  this is equivalent to 9.46 x 1012 km. The new cosmological findings congealed rapidly

  during the first decades of the twentieth century through a succession of other unexpected

  observations. It was realized that the universe was not only gigantic but also almost empty.

  Indeed, if one took all the matter of the observable universe and collapsed it into a pancake-

  shaped disk with the density of water, the thickness of this flat universe would be only

  one millimeter! As French mathematician and writer Blaise Pascal (1623–1662) wrote in

  Pensées of 1670, “Through space the universe grasps me and swallows me up like a speck;

  through thought I grasp it.”

  More surprises came. The biggest one: the universe is expanding (Chapter 5). Moreover,

  one strange property does not come up alone. During the 1930s, astronomers found out

  with puzzlement that the dominant form of matter in the universe is invisible. Galaxies are

  decoys for something that is unseen but more pervasive, which is weaving the fabric of

  cosmic space. Because this invisible mass does not emit or absorb light, it was named dark

  matter. I will show how images help unravel these surreal discoveries.

  These latest developments came about very quickly, resulting from observations by

  inquisitive minds using a succession of ever more powerful telescopes. However, the dis-

  covery of galaxies has been an amazing odyssey. Again, images were the bonfires lighting

  the path.

  Tools of Vision and of Measurements

  The appearance of vision in living organisms and the evolution of the eye have been remark-

  able processes. The retina of the human eye is the surprising achievement of some billions

  years of life evolutionary processes. Seven hundred million years ago, animals developed

  the light-sensitive protein opsin, which captures light. Since then, vision has taken multiple

  forms and provided animals of all kinds with a most efficient advantage.14,15 Aeons later,

  humans find themselves equipped with a liquid ball, a flexible soft lens, and 125 million

  photosensitive cells feeding a brain powerfully adapted for vision. Vision has provided us

  with an added capacity to adapt and survive, as well as to be creative and innovative enough

  to find stars, nebulae and explore the extragalactic universe. All this because we have eyes

  14 R. Dawkins, The Blind Watchmaker, New York: W. W. Norton & Company, 1996.

  15 Extinct trilobites had solid eyes made of calcite. See L.
Browers, Animal Vision Evolved 700 Million Years Ago, Scientific American Blogs, November 20, 2012.

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  assisted by a powerful brain to process the optical signals and the billions of photons that

  continuously hit the retina.

  We observe, astronomers observe. A simple statement attributed to the American base-

  ball player Yogi Berra (1925–2015) is most relevant: “You can observe a lot by just watch-

  ing.” Historians of science Lorraine Daston and Peter Galison set this out in more scholarly

  words: “Perceptions, judgments, and, above all, values are calibrated and cemented by the

  incessant repetition of minute acts of seeing and paying heed.”16

  Curiously, the topic of scientific observation itself has not received that much attention

  from historians of science. Hence the fine collection of essays assembled by Lorraine Das-

  ton and Elizabeth Lunbeck is quite unique and most enlightening. The essays show the

  evolution of the meanings and practices of observing and experimenting from antiquity to

  the early twentieth century.17 Learning to observe and to depict meant to acquire an ethos

  and a new way of seeing, as Daston explained. The methods of scientific observations as

  we know and understand them are relatively recent. Even during this period, they have

  evolved significantly, going initially from long lists and tabulations to include, with time,

  more details on set-ups, environments and conditions, bringing us finally to the modern-

  day metadata system. “By the turn of the eighteenth century, ‘observation’ had become

  an essential practice in almost all of the sciences, not just astronomy, meteorology, and

  medicine – and the complement and supplement of ‘experiment’.”18 As I will show, the

  opening of the world of galaxies benefited from this maturing process and pushed the cog-

  nitive demands of observing. Images, obtaining and interpreting them, played a crucial role

  in the deep transformation of astronomical observing, from the time of Galileo telescopic

  viewing to modern-day ‘machine’ science.

  Working Objects