Let’s talk about the beauty of space photography.
Alyssa Pagan has a lot to do with how beautiful the Carina Nebula looked in the first pictures from the James Webb Space Telescope. As a science visuals developer at the Space Telescope Science Institute, she is one of the people who turns the data that Webb collects into something that is not only visible but also beautiful.
Pagan says that the work is a “collaboration” of facts, scientifically-built aesthetic principles, and personal taste. This collaboration is needed for a number of reasons, not the least of which is that Webb is so far away from the objects being watched. The infrared spectrum is used by JWST to be able to see this far. Since people can’t see infrared, researchers like Pagan have to decide how to turn that data into something that can be seen. By figuring out what these choices mean, viewers can figure out a lot more than just how beautiful the picture is.
Pagan gets asked a lot of questions about things like the colours. JWST takes multiple exposures of narrowband data, which are very small ranges of wavelengths in the infrared spectrum that correspond to the presence of certain elements, like forms of hydrogen, sulphur, and oxygen. After that, they are colored based on a rule called chromatic ordering. Shorter wavelengths, like oxygen, are given to colours with shorter wavelengths, like blue, and so on. These are then put on top of each other to make the image’s base.
But because the hydrogen and sulfur bands are both red, the hydrogen is often given a yellower filter to make the final picture clearer. This makes what is called the “Hubble palette,” after the first telescope that made it popular.
People sometimes call these pictures “false.” But, Pagan says, the colors are based on real information. Scientists and non-scientists alike can read them like a map if they know how. In Webb’s picture of the Carina Nebula, for example, it’s clear that hydrogen and sulfur make up most of the lower red part, while oxygen makes up most of the upper blue part.
I love making things seem mysterious and out of this world.
After these base colours are put on, Pagan says, it’s “a matter of taste” what comes next. She could move the whole colour spectrum up or down, making blues look more purple or vice versa. Like with the Carina Nebula, the contrast will probably be made stronger, which will make the colors that go together stand out. There are also more objective changes, like cleaning up any artefacts like scattered light from the telescope, but at this point, two processors may come up with different images.
It’s not new to try to get people to feel something when they see pictures of space. Dr. Elizabeth Kessler, a scholar of visual culture, has literally written the book on how these images make us feel the sublime, which is a sense of awe at something that is beyond human understanding. One way they do this is by making us think of images we already know. In Picturing the Cosmos, she looks at how the artists on the Hubble team tried to make the vastness of space easier to understand by comparing it to landscapes.
This has been done this way with JWST as well. On the cover of Kessler’s book is a picture of the Carina Nebula that was taken by Hubble and was pretty closely copied by JWST. In the original, “hills and valleys” are used to describe the view. NASA refers to the new image in the same way, calling it the “cosmic cliffs” in a more casual way.
But presenting the Carina Nebula this way is also a matter of style.
Notably, there is no “up” in space, and while pictures taken from the ground usually show the north at the top, an orbital telescope has no idea what north means. Kessler points out that the image could have been turned around, which would have made the dust cloud look like it was “oozing off your screen.” Instead, it’s the cosmic cliffs, which look like something familiar instead of something strange and maybe scary.
The story had to be true. It seemed like there should be a mountain there.
Pagan wants to make the images “digestible” to the average viewer while keeping their magic. Kessler says that the comparisons used by image processors are “really useful. The size and scale of what we’re looking at are too big for us to understand. Mountains like these, which tower over us, are the closest thing we’ve seen to God.
Scientists and both professional and amateur astrophotographers use more than just the Hubble and Webb styles. Public science communicator Dylan O’Donnell says that it is popular with photographers on the ground in part because a narrowband approach helps to avoid problems with light pollution. The light from buildings and streets will flood a camera at ground level. But by cutting out everything except a very small band, “it lets people in the middle of a capital city take pictures that look like Hubble pictures,” says O’Donnell. But processors can figure out what these narrowband filters mean by using different colour palettes, just like they decide what to capture and how to do it. For example, the “CFHT palette,” which gets its name from the Canada-France Hawaii Telescope, is a popular way to do things.
The main difference between the Hubble palette and the CFHT palette is how difficult it is to order colors by hue. Hubble uses a yellower filter for hydrogen because it has a different possible wavelength. CFHT, on the other hand, moves sulfur up the colour spectrum, making green-purple nebulas that show different details. Heather Flewelling, an astronomer at CFHT, says, “It doesn’t change the science.” “It just makes some things stand out more.”
There are many different ways wavelengths and filters can be put together, and all of them result in different ways to show the data and different ways to look at it. O’Donnell made a preview tool that helps astrophotographers try out different techniques quickly and lets people who don’t know much about photography see the differences between the many options.
It’s up to you which filter you want to use. Even though O’Donnell says that most people like to stay as realistic as possible, his own work shows the benefits of using “false” colour to bring out the details, such as in his two pictures of the Eagle Nebula, one using true colour and the other using the Hubble palette. By comparing them, it’s clear that the second one is better for showing structure and depth. In the Hubble palette, the yellow-white dust stands out and looks much more detailed against the blue background. In the true color version, the different shades of pink look flatter and it is harder to figure out.
As useful as the Hubble palette can be, O’Donnell says that it can seem “a little bit clichéd” because it is used so often. He made popular a method that takes in both the green wavelength of visible light and the narrowbands for hydrogen and oxygen.
And the JWST itself is making pictures with colours that some people might not expect. Recently, several pictures of Jupiter came out, and the one that got the most attention made the planet look blue. Hubble took pictures of Jupiter that looked both blue and red at the same time. In the most recent picture, however, even the famous Red Spot looks white because it is reflecting sunlight. Pagan, who didn’t process this image, says that its colour scheme was probably meant to draw attention to the aurora, which does look red in contrast.
Kessler thinks this means that the Webb images might not keep following Hubble’s path so closely. “I’m interested to see what will happen,” she says. “If more people go that way,”
Webb’s future will be decided by a series of decisions made by both data and people. These decisions will be based on hundreds of years of visual culture and billions of years of light travelling through space.