The stunning appearance of the Carina Nebula in the first images from the James Webb Space Telescope is credited to Alyssa Pagan. As a developer of science visuals at the Space Telescope Science Institute, she is one of the wizards that translates data captured by Webb into something that’s not just visible but beautiful.
Pagan calls the work a “collaboration” of aesthetic data and principles built over decades of scientific study and personal taste. This cooperation is necessary for many reasons, not least the vast distances between Webb and the objects being observed. In order to see this far away, JWST uses infrared spectrum. Since people can’t see infrared, researchers like Pagan have to make choices about how to translate that data into something visible. By understanding these choices, viewers can decode much more information than just the pretty picture itself.
Colors, for example, are something Pagan often raises questions about. JWST captures multiple exposures of narrowband data, which means very small bands of wavelengths within the infrared spectrum that correlate with the presence of specific elements – forms of hydrogen, sulfur and oxygen. Then they are colored according to a principle called chromatic arrangement. Shorter wavelengths, such as oxygen, are assigned to colors with shorter wavelengths, such as blue, etc. Then they are overlaid to form the basis of the image.
However, because both the hydrogen and sulfur bands are associated with shades of red, hydrogen is often given a yellow filter to produce sharper detail in the final product. This results in the “Hubble Panel” – so named because it was popularized by the older telescope.
These images are sometimes called “false” colors. But, Pagan emphasizes, the colors represent real data. With the right knowledge, both scientists and ordinary people can read it like a map. In the Carina Nebula’s web image, for example, the lower red portion is clearly dominated by hydrogen and sulfur, while the upper blue portion is dominated by oxygen.
“I especially enjoy making things look more ethereal and magical”
After applying these primary colors, Pagan says, things become “a matter of taste.” You may shift the entire palette up or down the spectrum, making the blue look purple, or vice versa. Contrast is likely to increase, as in the case of the Carina Nebula, making complementary colors pop. There are more objective changes made as well, such as cleaning up any artifacts such as scattered light from the telescope, but at this point, two processors might come up with different images. “I especially enjoy making things look more ethereal and magical,” says Pagan. “There’s a whimsy in my approach – because it’s space!”
Efforts to evoke not only a rational but an emotional response to images of space are not new. Visual culture scholar Dr. Elizabeth Kessler has written a book about how these images evoke the sublime — a sense of awe of something beyond human comprehension — in part by associating them with images we are already familiar with. in photography of the universeinvestigates how the visual developers on the Hubble team attempted to make the vastness of space understandable by visually linking them to the landscape.
This practice continued with the JWST. Kessler’s book cover image is a Hubble image of the Carinae Nebula, which has been reproduced fairly closely by JWST. Originally, the view was described as depicting “hills and valleys”. The new image is referred to in similar terms, colloquially called “cosmic cliffs” by NASA.
However, presenting the Carina Nebula in this way is also an aesthetic decision. Talking to the edgeKessler highlights planting and routing decisions. “There are many areas [within the nebula] Where you can show the birth of stars. But they chose this area and configured it in such a way that the edge of the cloud creates this horizon line, she says.
Notably, there is no “higher” in space, and while images from Earth often orient their images so that north is at the top, north is meaningless for an orbiting telescope. Kessler notes that the image could have been directed in the opposite direction, turning the dust cloud into something that “comes out of your screen.” Rather, it’s the cosmic cliffs, which reflect something more familiar than bizarre and potentially repulsive.
“The trend was set largely at first because it felt more natural,” says Pagan. “It has to be grounded. I felt like it had to be a mountain.”
Pagan’s goal is to make images “easy to digest” for the everyday viewer while still maintaining their charm. The analogies with image processors, Kessler says, are “really useful. The scale of what we’re looking at, the enormity of it, is beyond human understanding. The closest thing to our experience are things like these mountains looming above us.”
The Hubble and Web aesthetic is not the only way that professional and amateur astrophotographers take it. It’s popular with photographers on the ground, in part, according to general science mentor Dylan O’Donnell, because using a narrow-band approach helps avoid problems with light pollution. The camera on the ground floor will be flooded with light from buildings and streets. But by excluding everything but a very small band, “it allows people in the middle of the capital to take Hubble-like images,” says O’Donnell. But, just as they make decisions about what to capture and in what direction, processors can use a variety of color palettes to interpret narrow band filters. For example, another popular approach is the “CFHT panel,” named after the Canada-France-Hawaii Telescope.
The differences between the Hubble panel and the CFHT panel mainly come from multiples of the chromatic arrangement. While Hubble gives hydrogen a yellow filter based on a different potential wavelength, CFHT instead pushes sulfur up in the color spectrum, resulting in a purple-green nebula that brings out different details. “It doesn’t change the science,” says CFHT astronomer Heather Flewelling. “It makes some features more obvious.”
There are many different possible combinations of wavelengths and filters, all of which lead to different ways of displaying data – as well as different aesthetic experiences. O’Donnell has created a preview tool that helps star photographers quickly try different approaches and lets everyday people see the difference between the many options.
Choosing between filters is a matter of preference. While O’Donnell says most people prefer to stay as natural as possible, his own work also highlights the benefits of using “pseudo” color to bring out detail, as in his two images of the Eagle Nebula – one using true color and one using the Hubble palette. By comparing them, the benefits of the latter to show structure and depth become apparent. Yellow and white dust stand out and appear more detailed against a blue background in the Hubble panel, while different shades of pink in the true-color version appear flatter and more difficult to analyze.
As useful as it can be, O’Donnell says the Hubble panel can look “a little tacky” due to its common use, and he personally popularized a synthetic approach that captures the wavelength of green visible light along with narrow bands of hydrogen and oxygen.
JWST itself also produces images in colors that may be unexpected for some. Recently, several images of Jupiter have been posted, with headlines making the planet appear blue. Although Hubble captured images of Jupiter at the same time in blue and red, in the latest image, even the famous red spot appears white due to the reflection of sunlight. Pagan (who didn’t process this particular image) says the color palette was likely intended to highlight the aurora borealis, which appear red by contrast.
For Kessler, this suggests that Webb’s images may not continue to closely follow Hubble’s path. “I’m curious to see what will come of that,” she says. “If there is more it will go that direction.”
Webb’s direction will be a series of decisions made by data and people together, a combination of centuries of visual culture – and billions of years of light traveling through space.
Originally published at San Jose News Bulletin
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