The astronomical sublime
Part of a visual tradition that reaches back to Romanticism, images from the Hubble Space Telescope awe as they inform.
A dark cloud against a background of orange and blue reaches upward, stretching nearly to the top of the frame that contains it. Brightly backlit at its top and outlined throughout with a soft glow, the sinuous shape claims the viewer’s attention with its majesty and grace. But the closer one looks, the more difficult it becomes to classify what is pictured. Because of its wispy outline and top-heavy proportions, it appears that the form must be composed of something airy, something gaseous and insubstantial; however, its elongated profile resembles none of the clouds seen above the earth, and its blackness surpasses that of even the most threatening storm. Its color and assertive vertical orientation instead suggest a gravity-defying geological formation carved into a twisting pillar by unknown forces and silhouetted against a bright sky. The object almost oscillates before the viewer: cloud and landscape, familiar and alien.
The image is one of the many compelling views of the cosmos credited to the Hubble Space Telescope since its launch in April 1990. The National Aeronautics and Space Administration (NASA) and the Space Telescope Science Institute (STScI), the research center that manages the instrument, released the image of the Eagle Nebula (right), along with one of the Whirlpool Galaxy (see photo below), to celebrate the orbiting telescope’s 15th anniversary in April 2005. The view of the Whirlpool is less ambiguous than that of the Eagle; its distinctive spiral shape is iconic, the recognizable sign of a star system akin to the Milky Way. It is, however, no less powerful an image than the representation of the Eagle Nebula. The dynamic whirl pulls the eye along pathways dotted by red stars into the galaxy’s brilliant yellow center. The subtle blues of its arms contrast with the warmer yellows and reds of the stars. As with the Eagle Nebula, the celestial object nearly fills the frame, conveying a sense of its vast size and scale. And for both images, the most highly resolved versions reveal incredible, even overwhelming, levels of detail.
From its orbit above our globe, the Hubble Space Telescope has provided a revolutionary view of the cosmos. Freed from the obscuring atmosphere of the earth, the instrument has allowed astronomers to observe with new clarity, thereby enabling an improvement in seeing that is often compared to Galileo’s first use of a telescope in the 17th century. Because the Hubble holds a seminal place within contemporary astronomy and its images have circulated widely—to near-universal acclaim—its views of the cosmos have become models for images delivered from telescopes. Hubble images have also shaped depictions of the universe in popular culture, and it is common in science fiction films, TV shows, and video games to see spaceships fly through Hubble-inspired scenery.
This view of the Whirlpool Galaxy was released to mark the telescope’s 15th anniversary, April 25, 2005. (Courtesy NASA, ESA, S. Beckwith, and the Hubble Heritage Team [STSCI/AURA])
In the more than 20 years since NASA released the first blurry, black-and-white Hubble image, astronomers have developed representational conventions and an aesthetic style. The archive of Hubble images demonstrates that scientists have come to favor saturated colors, high contrast, and rich detail as well as majestic compositions and dramatic lighting.
Such images now define how we visualize the cosmos. They do not look like older photographs of the stars, nor are they anything like what can be seen in the sky on a dark night. Yet they appear to present the universe as one might see it, previewing what we imagine space explorers and tourists may experience when manned space travel extends humanity’s reach beyond the earth’s orbit. Improved technology, a telescope orbiting high above the earth’s atmosphere, and sensitive digital cameras can seem an adequate explanation for their brilliant hues and sharp resolution. But there is more behind the images than the workings of advanced instruments. The appearance of the Hubble images depends on the careful choices of astronomers who assigned colors, adjusted contrast, and composed the images. Although attentive to the data that lie behind the images, through their decisions astronomers encourage a particular way of seeing the cosmos.
As with the Eagle Nebula, many of the Hubble images bear a striking resemblance to earthly geological and meteorological formations, especially as depicted in Romantic landscapes of the American West. In the late 19th century, the painters Thomas Moran and Albert Bierstadt as well as the photographers William Henry Jackson, Timothy O’Sullivan, and others portrayed the awe-inspiring and unfamiliar western scenery in the visual language of the sublime. The formal similarities between these two sets of pictures situate the Hubble images within a visual tradition, and the reference to the sublime also has philosophical relevance. As defined by Edmund Burke and Immanuel Kant, the sublime describes an extreme aesthetic experience, one that threatens to overwhelm even as it affirms humanity’s potential.
For Kant, the sublime arises out of a tension between the senses and reason, and each faculty must be engaged to experience such an intense response. The Hubble images invoke the sublime, encouraging the viewer to experience the cosmos visually and rationally, to see the universe as simultaneously beyond humanity’s grasp and within reach of our systems of knowledge. This tension extends to the relationship between the images and the celestial objects they represent; their reliance on digital data and imaging, which brings together numeric and pictorial representations; and the symbolic significance of the landscape reference with its evocation of the frontier. By repeatedly making use of this tension, a fundamental attribute of the sublime experience, the Hubble images make claims not only about what we know of the cosmos but about how we gain knowledge and insights.
Typically, interest in a scientific mission lasts only briefly. But decades after the telescope’s launch the Hubble’s images still made headlines and circulated widely online and in print. They achieved an almost unparalleled popularity within the history of astronomical images, even within the history of scientific images. Many of the best-known Hubble images were made in an effort to reach those who are not scientists, and those involved with their production and distribution, from astronomers to public relations officials at STScI to administrators at NASA, acknowledged that they hoped the eye-catching images would encourage continued financial support for the Hubble Space Telescope, NASA, astronomy, and scientific research more generally. As a result, some dismiss the aesthetically developed Hubble images and their evocation of the sublime as little more than hype and visual hyperbole, and consider them nothing more than crass attempts to curry public favor.
Aesthetics can seem secondary at best and often unnecessary to the scientific project. If science strives to master with precision and exactitude the physical processes at work in the universe, if it ultimately seeks to enhance the human condition through improving and extending life, aesthetics can seem a messy distraction from its larger goals. At times, astronomers have argued against dedicating significant resources to making attractive pictures, suggesting that images might be valuable public relations tools, but data—unambiguous numeric values and measurements that could be logically analyzed, be compared with other data, and lead to carefully reasoned conclusions—were the intended output of the Hubble Space Telescope. If “pretty pictures,” a phrase often used by astronomers, do not forward the quest of science in the purest sense, the production of such images was little better than a diversion.
The famous view of the Eagle Nebula that is often called the “Pillars of Creation.” The stair-step shape of the image is caused by a difference in resolution in a camera sensor. (Courtesy NASA, J. Hester, and P. Scowen)
Those who study the visual culture of science have also entered into these debates. The art historian James Elkins [AM’84, MFA’84, PhD’89], who has written extensively on the relationship between art and science, has been emphatic in his dismissal of scientific images made for public display, seeing such pictures as contributing to what he calls “astronomy’s bad reputation” for producing flashy but scientifically uninteresting images. Elkins sees these images as a distraction from what he considers to be far more interesting images, namely those that scientists use only for the acquisition of knowledge. Elkins is correct that scholars of visual culture often ignore images that show a distant celestial object in only a few pixels. But he too quickly pushes aside the colorful views that reach a larger audience and too strongly judges them as lacking in value. To regard them as little more than overwrought marketing materials ignores the depths of their connections to the practice of science as well as how profoundly the images shape our cultural imagination.
The astronomers who develop Hubble images attempt to balance the often contradictory demands and interests of an audience that ranges from fellow astronomers to schoolchildren. As they craft the images, translating sometimes invisible attributes of the data into visible form, they strive to make the images scientifically valid and aesthetically compelling. The resulting Hubble images have served many functions: they document and record data; aid scientists in their effort to understand their observations; influence decisions about support for science; and inspire aesthetic responses from a variety of audiences.
The Eagle Nebula and Whirlpool Galaxy images were crafted by members of the Hubble Heritage Project, a group of astronomers and image processing specialists at STScI whose purpose is to develop aesthetically attractive images. Since its formation in 1997, the Heritage Project has released a new image almost every month, and its work has resulted in an archive of vividly colored and dramatically detailed views of nebulae, galaxies, and other celestial phenomena. The collection supplements and expands the body of images astronomers produced for their research programs or those developed for NASA press releases. The Heritage Project has played a significant role in defining how Hubble images “should” look.
In many ways, astronomy is about the pleasure of looking. The hallways of observatories and university astronomy departments are filled with brightly colored images made from Hubble data as well as other sources. The prominence of images not only attests to their importance within the discipline but also suggests that they have an inescapable influence on how astronomers imagine the heavens. And the engagement of scientists with ways of seeing and presenting the universe testifies to the essential place of aesthetics within any attempt to comprehend the cosmos, understood in the broadest sense of the term as an ordered and harmonious system.
Reference to the familiar visual iconography of 19th-century landscapes of the American West threads through the Hubble Heritage Project’s efforts to reach a broad audience. The comparison of Hubble images and Romantic landscapes begins with their shared features, similarities in appearance that link two sets of images made more than a century apart: their color palettes, a focus on small regions within larger objects, dramatic backlighting, towers and pillars, a sense of overwhelming size and scale. A rich and ideologically complex culture informed scientists’ efforts to translate data into images of nebulae, galaxies, and star fields. Rather than creating something entirely new, astronomers working in a period of great technological change extended an existing mode of visualization and representation—one associated with exploration—to a new phase of discovery. The mythos of the American frontier functioned as the framework through which a new frontier was seen.
In many ways, the Eagle Nebula and Whirlpool Galaxy images exemplify the ways in which the Hubble images circulate and function in the world. They also resonate with the history of the Hubble Space Telescope and the longer history of astronomical observing. A 1995 image of the Eagle Nebula, often called the Pillars of Creation (above), was released nearly ten years before the anniversary image. It focuses on a different region of the nebula that features a set of ambiguous columns also resembling both clouds and landscape formations. Perhaps more than any other Hubble image, that first dramatic view of the Eagle Nebula revived the telescope’s reputation after the devastating discovery in July 1990 that its optics were flawed, and the image remains widely admired. Although observed with a different camera and exhibiting subtle visual differences, the later Hubble image of the Eagle Nebula pays homage to the first.
The view of the Whirlpool Galaxy looks further back into the history of astronomy and alludes to images that recorded the discovery of the distinctive shape of galaxies. In the 1840s, Lord Rosse, a wealthy amateur astronomer and engineer, built a giant six-foot telescope, aptly dubbed the Leviathan, on his Irish estate. The largest instrument of its day, the audacious structure was a landmark in a long tradition of building ever more impressive instruments to collect light from the distant reaches of the universe. The cloudy nights of Ireland limited its use, but Rosse and his assistants made an extremely valuable discovery when they observed that the glowing cloud known as M51 had a spiral shape, a form they also found in some other nebulae. Drawings and engravings of the newly dubbed “Great Spiral” circulated widely, and the revised perception of the universe made it possible for astronomers to imagine that the Milky Way did not comprise the entire universe. By revisiting the object that was pivotal in advancing science’s notion of the cosmos, the Hubble’s image of the Whirlpool underlines the value of building ever better instruments for observing.
The Eagle Nebula and Whirlpool Galaxy images were planned and crafted while NASA administrators debated the safety of a final space shuttle mission to repair the Hubble. As such the pictures not only represented two well-known celestial phenomena but also made a plea for the continued support of the instrument by displaying its capabilities in brilliant color and exquisite detail. Most people without advanced degrees in astronomy are hard-pressed to identify exactly how the Hubble Space Telescope has changed and enhanced humanity’s understanding of the cosmos. They have, however, seen many examples of the Hubble’s dramatic pictures, images that NASA showcases on its websites and that also appear on calendars and coffee mugs, album covers and art museum walls. Such pictures serve as visible evidence of the Hubble’s success. More than any notion of what astronomers do with the Hubble’s data, the stunning images account for the public’s support and affection for the telescope.
When releasing the anniversary images, NASA and STScI went to exceptional lengths to reach different audiences. Beyond the usual announcements, the STScI press office distributed more than 100 large prints, four feet by six feet for the Whirlpool Galaxy and three feet by six feet for the Eagle Nebula, to planetariums and science museums throughout the United States.
In anticipation of any questions that might be raised about using an oversubscribed instrument with a limited life span to make pictures for museum walls, the data for the Whirlpool Galaxy were also released in a format that made them readily usable by researchers. Because of its large size and relative proximity to the earth, observing the entire galaxy required six separate pointings of the telescope, and at each pointing several observations were made with four different filters. The total data set included 96 distinct exposures that were pieced together to create the image. Typically, astronomers must do the work of generating a composite for any observations they oversee. By providing the processed data, STScI saved scientists the time and effort they would need to expend before they could begin to analyze the data, to say nothing of the time put into submitting a proposal to use the Hubble. As well as making the task of scientists easier, STScI invited them to publish research papers on the Whirlpool Galaxy.
The existence of these distinct modes of representing the Whirlpool Galaxy points toward a fundamental duality within every Hubble image, even the prettiest ones. Each image is expressed first as data and then translated into pictorial form. Hubble images are mediated several times over. Their appearance depends on the advanced optics of the telescope and its sensitive digital detectors, computer software programs that pictorially represent data, and the human operators who use them, thereby adding their aesthetics and scientific sensibilities. Each layer of mediation raises important questions about how these images represent the cosmos.
Neither the Eagle Nebula nor the Whirlpool Galaxy images exactly mirror the celestial objects they depict, and the images could look differently than they do. The sensitive digital cameras aboard the telescope numerically record subtle differences in light intensity that are too fine for the human eye to discern. The cameras also register light beyond the visible range, extending into ultraviolet and near-infrared. By using special filters the telescope collects different wavelengths of light, in effect recording the presence of certain colors but always monochromatically. In their rawest pictorial form, Hubble images are black and white, often lacking in clear detail, and covered in white streaks (the traces of high-energy rays bombarding the telescope in its orbit). For large objects, as is the case for the Whirlpool Galaxy, a single image shows only a small portion of the larger whole. To produce the highly polished images for which the Hubble is famous, astronomers must make a series of decisions that combine scientific interests with aesthetic concerns.
A great deal rests on how the Hubble images look. The Eagle Nebula and Whirlpool Galaxy images illustrate in concentrated fashion the diverse threads that can be teased out of their appearance. The Hubble images evoke an experience of the sublime as they allude to the landscapes of the American West. They also engage with the history of astronomy and of observing the cosmos by looking back to past observations of these objects. They participate in debates about how best to observe and represent the universe, commenting on and ultimately influencing NASA’s decisions about their very means of production.
In the end, the Hubble images not only look like the earthly landscape, they also reflect the complexity of scientific observation. The greatest discoveries come from inviting reason and the senses, the rational mind and the aesthetic response, to ignite and affirm each other.
Elizabeth Kessler teaches at Stanford University. She has been awarded fellowships by the Smithsonian Institution National Air and Space Museum and Stanford. This story is adapted from her book Picturing the Cosmos: Hubble Space Telescope Images and the Astronomical Sublime with the permission of the University of Minnesota Press. Copyright 2012 by the Regents of the University of Minnesota.