American Scientist

Our understanding of nature has always relied heavily on signs, be they words, equations, graphics, or the cuneiform incisions used for six centuries by Mesopotamian astronomers to signify celestial movements. We use signs to sample and reduce the complexity of phenomenal reality into understandable terms. At their best, these methods can cut through noise to reveal signal, yielding important truths about the universe.

Yet this transliteration contains rich opportunities for misapprehension and misunderstanding. As physicist Werner Heisenberg wrote, “What we see is not nature herself, but nature exposed to our method of questioning.” And he went even further, warning that “contemporary thought is endangered by the picture of nature drawn by science. This danger lies in the fact that the picture is now regarded as an exhaustive account of nature itself so that science forgets that in its study of nature it is studying its own picture.”

Heisenberg didn’t offer an alternative, though, because one doesn’t exist. No better plan presents itself. The best that we can do is to keep improving and superseding our signs. Nowhere is this more evident than in the history of astronomy, where a procession of graphic images has opened our eyes to the scale of the universe and to our position within its staggering immensity—a process that still continues with deep-field astronomical images and supercomputer data visualizations that bring within our visual grasp cosmic structures spanning hundreds of millions of light-years.

Long before the telescope, and even longer before the invention of photography, the eye and hand of the observer were significant assets to a working astronomer. By the Middle Ages this work was already initiating what architectural theorist Dalibor Vesely has called the “mathematization” of observable reality. It is beautifully encapsulated in a hand-drawn grid found within the 1121 encyclopedia Liber floridus (“Book of flowers”), an early example of what we today would call an infographic.

Liber floridus, compiled by Lambert of Saint-Omer in what is now northern France, ranks as the first Encyclopedia of the High Middle Ages. Inscribed upon its parchment is an illustration titled simply “Seven Planets.” Its zigzagging lines depict the motions of the five visible planets known since ancient times, plus the Sun and the Moon, all shown in relation to the latitude lines of the zodiac. The Sun is depicted as a bright flower, the Moon as a crescent, and the planets as smaller, blossomlike forms. The arrival of such an abstracted display of quantitative information in a pre-Gutenberg manuscript carries with it something of the same shock as if one had spotted a gleaming glass office tower sprouting among a sprawl of half-timbered medieval buildings.

This depiction of planetary motions is a visual scaffolding only, but other parts of Liber floridus place those motions within the framework of the cosmology of the time. For close to 2,000 years, our conception of the universe’s design was based on Aristotle’s geocentric model, with the Sun, Moon, planets, and stars arranged in neatly nested spheres, with Earth at the center. The iconography associated with this model was deeply embedded in the human imagination. Nicolaus Copernicus’s famous and elegantly simple heliocentric Solar System, taken from his 1543 book De revolutionibus orbium coelestium (“On the revolutions of the celestial spheres”), closely resembled many similar depictions from prior centuries—similar, apart from the Sun now occupying the center. In a graphical sense, the Copernican Revolution mostly involved switching the placement of the Sun and Earth as the center of the cosmos.

Window to Infinity

Just as Copernicus’s depiction of a Solar System for the first time can, on cursory inspection, seem practically indistinguishable from many preceding depictions of an Earth-centered cosmos, so is British astronomer Thomas Digges’s woodcut print, titled “a perfit description of the Coelestiall Orbes” (see figure below). Produced in 1576, only 30 years after the publication of Copernicus’s book, at first glance the print seems little more than a dutiful iteration of the Polish astronomer’s vision. Examined more closely, however, the print reveals a radical break even with Copernicus.

Whereas Copernicus had retained the ancient notion that, like the planets, the stars revolve on an outermost sphere, Digges made an audacious conceptual leap. He conceived that the Sun blazing at the Solar System’s center is actually a star, simply one among innumerable “perpetuall shininge glorious lightes” glowing in the heavens. His print was simultaneously the first published presentation in England of Copernicus’s heliocentric vision, and the first map anywhere that clearly shattered that outermost crystalline sphere. It positioned the Solar System within a much greater, even boundless expanse. Something like our contemporary view of the cosmos was being born.

After the invention of the telescope, the importance of graphic images in astronomy only increased. Galileo Galilei in a sense anticipated the future marriage of photography and astronomy when he constructed one of the first helioscopes—a device capable of projecting a focused beam of sunlight from his telescope’s eyepiece onto a piece of paper. This invention permitted him to track and to trace the evolution of dark spots as they panned across the Sun’s surface as it rotated. When converted to etchings, Galileo’s solar images have a proto- photographic, three-dimensional quality to them. The visual history of astronomy, previously largely devoted to schematic and sometimes allegorical representations of the sky, was becoming more purely representational.

The authenticity and power of astronomical images, in turn, began to escape the confines of their specialized field and migrate into the realm of purely visual art. More than two centuries after the first use of a telescope to observe the sky, Anglo-Irish astronomer William Parsons, the Earl of Rosse, funded the construction of a six-ton telescope with a 72-inch aperture in his residence at Birr Castle, County Offaly. Inaugurated in 1845, “the Leviathan of Parsonstown” was so powerful that on rare nights of cloudless Irish skies the Earl was able to discern an intriguing spiral structure within what was then believed to be a nebula inside the Milky Way.

A print based on Parsons’s careful drawing of this object caused a sensation when it was reproduced in the United Kingdom. By 1879 it had made its way into a best-selling book by French astronomer Camille Flammarion, a copy of which is thought to have been acquired by the library of the Saint-Paul de Mausole Asylum in Provence, France. Between 1889 and 1890, one patient of that asylum, a then-unknown Dutch artist who had razored off his left ear in a fit of rage, conducted a voluminous correspondence with his worried brother on many subjects—including astronomy, which clearly fascinated him. He also produced many extraordinary paintings. Parsons’s drawing apparently inspired the kinetic pinwheel careening across the center of what is probably the best-known artistic rendition of the night sky: Vincent van Gogh’s Starry Night.

Beyond and to the right of a tormented cypress tree, that swirling double vortex defines the painting. Historians of astronomy and art both widely accept that the vortex is a translation of Parsons’s illustration of what we now call the Whirlpool Galaxy—a spiral system of stars interacting with its smaller companion. The true identity of the Whirlpool and other galaxies like it was not uncovered until less than a century ago, when Edwin Hubble determined that they lie far outside our Milky Way galaxy. Parsons saw the signs, but did not know how to interpret them.

Art of Discovery

As with mapmaking during the Age of Exploration, the graphic image largely played a supporting role within astronomy prior to the 20th century, codifying discoveries already made. But with the marriage of telescope and photography, images themselves began to yield genuinely new insights. The vast majority of discoveries in observational astronomy over the past century have been the result of photographic processes, not least of them Hubble’s recognition of the existence of other galaxies.

The proof came when he detected a special type of flickering star, called a Cepheid variable, in a glass photographic plate of the Andromeda “nebula.” The rate at which a Cepheid flickers indicates how luminous, and hence how far away, it is. Such changes would be imperceptible to the eye alone, but with the aid of photography, the astronomer was able to see his answer. Prior to that moment, it was still possible to believe that the Milky Way was the observable universe. Hubble realized it was just one among a vast congregation of galaxies scattered across the vastness of space, and he wrote “VAR!” for “variable,” directly on the plate in red ink.

Starting in the 1980s, such glass plate negatives were replaced by powerful light-gathering charge-coupled devices, or CCDs—digital photon detectors whose acute sensitivity is further increased through the use of extended time exposures. With their help, digital surveys made it possible to map out the structure of the cosmos, showing not just galaxies but clusters of galaxies and even larger matrixes of multiple galaxy clusters. At the same time, supercomputers permitted graphic translations of these enormous formations.

In 2014, a team led by University of Hawaiʻi astronomer Brent Tully converted a database containing the velocities of thousands of galaxies into a supercomputer visualization of a cube of space 500 million light years across (see figure above; animated versions available here). Their graphic, which translated the velocity measurement into a 3D depiction of galaxy density and motion, allowed them to identify what they named the Laniakea Supercluster—Hawaiian for “immeasurable heaven.”

Laniakea encompasses the Milky Way along with about 100,000 other galaxies. It is the largest known structure that we live in, other than the visible universe itself. In effect, Tully and his collaborators have provided us with a new home address: Earth, Solar System, Milky Way, Local Group of galaxies, Virgo Cluster of galaxies, Laniakea. In this and other recent cases, visualization preceded discovery, permitting the discernment of structure and yielding profound understandings about our place in nature’s order.