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science: cosmos vs. canvas
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Cosmos vs Canvas
Art and science collide, then dance a minuet, in popular astronomy images
by Jayanne English

Bold colour images from telescopes act as extraordinary ambassadors for astronomers because they pique the public’s curiosity. But are they snapshots documenting physical reality? Or are we looking at artistic space-scapecreated by digitally manipulating astronomy images? Actually, neither description is totally accurate. Rather, each image is a battlefield where attempts by scientists to represent their discoveries tend to all but drown out the conventions of visual literacy. Astronomers devise visual codes that they believe emphasize the physical characteristics of an astronomical object. But rarely do they employ the kind of artistic techniques — colour contrast and composition, for example — which might produce a more engaging image with greater clarity for the non-expert public. Fortunately, though, sometimes in this battle between the cultures of science and visual art, both sides win.

Most astronomy images are not meant to be one-to-one analogs with respect to visual reality. This statement applies equally to both scientists and artists who are involved in the visualization of astronomical data. However, each group of practitioners has a different agenda that reflects their culture. For example, most scientists believe that the visual grammar of the picture — that is, the collection of compositional elements affecting the interpretation of an image — is irrelevant, at least compared to the importance of following standard conventions of astronomical science when choosing image orientation and other visual attributes. This attitude arises, in part, because images made by astronomers are typically meant to be shared with colleagues, rather than the public.

While astronomical data has occasionally been acquired for specific use in public outreach (newspapers, magazines and textbooks, for example) in the past, recent outreach images have almost always been appropriated from research. A new trend is to borrow hard data acquired for scientific purposes and convert it into images for popular magazines and the like. Contemporary astronomy image-makers therefore generally appreciate that their renditions should, if possible, intrigue the non-scientist as well as the researcher. However, since most astronomy image-makers (including myself) are scientists, they tend to feel primarily obligated to articulate the scientific meaning inherent in the data. And, unfortunately, most astronomers hold the misconception that if this is accomplished, then the image will automatically be engaging to anyone. I therefore find it necessary to advocate strongly on behalf of the communicative power of visual literacy, and recommend that persons with a passion for it be included on image-making teams.

Visualization Stages
The tensions that arise between the two cultures of science and art during the production of a single astronomy image can be well illustrated by describing the various stages that images go through during data visualization.

Let’s begin by considering the original black and white data gathered by NASA’s Hubble Space Telescope (HST), and in particular how the HST’s observations are converted into colour images appropriate for gracing the pages of popular astronomy magazines. Aboard the Hubble, digital light detectors (like those in a digital camera) are used to measure the amount of light emanating from a particular section of the sky. However, it is worth noting that it is not actually possible to create colour images using the HST that would match what our eyes would see in the same region of space. This is because, in order for these digital sensors to be sensitive enough to discern the faint light of astronomical phenomena, they do not record in colour. Instead, a succession of filters are used to capture the same piece of sky several times. Each filter selects for different portions of the electromagnetic spectrum, so that each resulting black and white exposure represents the particular range of electromagnetic energy or “colour” allowed to pass through that particular filter. Of course, in addition to visible light, the HST’s filters can also select for ultraviolet or infrared ranges of the spectrum. Our eyes do not normally see these ranges, and so these exposures have no “intrinsic” colour.

The first stage of image manipulation involves altering the intensities (ie, brightness) of these black and white filtered visuals using one of a variety of mathematical “stretch” functions which adjust the image to allow the viewer to see very faint and very bright regions simultaneously. Unfortunately, this act destroys the ability of the image to communicate accurate information about the actual amount of light coming from any particular astronomical object. So, after this manipulation has been performed, no physical scientific measurements can be made from the image at all. It has already become something closer to an illustration than a factual observation.

Producing a coloured image from the black and white originals usually involves selecting three or more stretched images from different filters/energy ranges. For example, data from the ultraviolet, blue, green, and infrared portions of the electromagnetic spectrum might be used. A colour (any colour, in fact) is assigned to each black and white image, and the coloured versions are overlapped to form a multicoloured image. Because more than one combination of colours is both possible and valid, it is common to create a few different multicoloured renditions. (For HST images, the selection of which version will be released to the public as “official” is often determined by a committee.) Finally, the contrast of the multicolour image is fine-tuned, the image is cropped, and an orientation (that is, which way appears to be up) is selected.

For an excellent further explanation of how HST images are manipulated, visit The Meaning of Colour, an online interactive feature of the “Behind the Pictures” section of the HST’s official outreach Web site (www.hubblesite.org). Visitors to the site can play with different combinations of single colour Hubble images, overlapping them one-by-one in order to view the final result.

Art and Science Diverge...
It is at the stage where colours are selected for black and white images that one first begins to notice the differing respective influences of the cultures of science and art. For example, imagine that two different filters have been used to pass light of two different energies (i.e., wavelengths) — both in the red part of the spectrum — to the human eye. Because wavelengths of light can vary with the temperature of the object that emitted them, these energies are often indicative of two different temperatures. Understanding this natural relationship, the scientist will tend to automatically colour the hotter one blue (for higher energy) and the cooler one red (for lower energy). Then, even if the light from a third filter is intrinsically blue (i.e., much hotter), they may assign green to that exposure. Or, they may decide to use another combination of colours which still follow the same colour/temperature principle, such as blue for the image from the blue filter, green for the warmer red filter image, and red for the cooler red filter image.

On the other hand, an artist intent on communicating with the public might instead select colours with the goal of giving the image some appearance of spatial depth. If they want to make a certain feature (perhaps a star or gas cloud) appear closer to the viewer, the artist might note that its light corresponds predominantly to one of the filters. By colouring this filter red, and the other filters green and blue, everything but the chosen feature (and other features with the same colour energy) would sink into the background.

Clearly neither the scientist nor the artist wants to create a one-to-one analog of reality as defined by human vision. In fact, the scientist’s approach often reduces the image to something akin to a colour contour plot — their images are often more like a globe with all the countries painted in different colours than a photograph of the earth taken from space. Meanwhile, the artist’s goal is to engage the viewer and hold their attention, which endangers the scientific accuracy of their renditions. I believe that the most striking astronomical images occur when the goals of both artists and scientists are balanced. When this happens, both sides win.

... and then Converge Again
While I will continue to generate images using data from the HST (for both outreach and scientific purposes), I’m even more excited about my recent work creating colour vistas of the “invisible” universe — a universe revealed in radio telescope data collected by the Canadian/International Galactic Plane Survey (I/CGPS) using the Dominion Radio Astrophysical Observatory array in Penticton, B.C. The I/CGPS is exposing the “stuff” between stars, revealing remarkable new features in our Milky Way Galaxy, and presenting scenes that do not correspond, visually speaking, with how we usually imagine the sky to appear.

As it covers a range of electromagnetic radiation invisible to the human eye, the visualization of this data is not constrained by expectations of true colour. Thus, my goal is to take the unseen and display it with sufficient presence that it can be visually apprehended as real, which of course it physically is.

An example of both art and science meeting their goals, and winning, happened recently during the creation of an I/CGPS radio astronomy image revealing the Cygnus Region — a region of the Milky Way Galaxy that is being energized and recycled by the creation and destruction of massive stars. (See the images associated with this essay.) Glowing filament-like clouds of dust (blue and turquoise) and gas (green) extending between stars compose the interstellar medium. Bright compact nodules of this same gas (white) cradle newborn stars, and extended gas shells (yellowish and red) mark the sites where stars have died. My image Vista of the Cygnus Region is a combination of art and science approaches: Colours were selected to match the trend in energies of the four data sets used (which pleased the scientists), but each colour was allowed to deviate from a pure hue in order to enhance colour composition and lend a feeling of depth to the image (which pleased the artists).

Jayanne English is an artist and astronomer who holds a diploma from the Ontario College of Art and Design, and a PhD in Astronomy and Astrophysics from Australian National University. Her forte is the creation of colour images for popular audiences. She has expressed her ongoing commitment to public outreach as astronomy columnist for CBC’s Quirks and Quarks (2000-2002) and coordinator of NASA’s Hubble Heritage program (1998-2000). Jayanne is presently an Assistant Professor at the University of Manitoba.

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