Imagine zipping around the Carina nebula. Featured among the new images from the James Webb Space Telescope, the plume-y clouds act as a “stellar nursery” where stars are formed.
You’d see some bright infant stars, and glowing gas; perhaps it would look pinkish, or white. But you wouldn’t see the blue or terracotta featured in the NASA photos. That’s because the JWST images aren’t your standard photographs. They’re the product of some nifty processing.
The images from JWST like the one of the Carina nebula and the deep field image are composed from data from the infrared spectrum, which has a longer wavelength than visible light, and is sometimes called “heat radiation.” Infrared radiation isn’t just an outer space thing—you and I give off infrared light, too. Some animals, like snakes, can see infrared light through specialized organs, but human cells in the retina aren’t adapted to seeing infrared (except under very specific circumstances, or with the assistance of night vision goggles). Humans can only see a fraction of the electromagnetic spectrum with the naked eye. This fraction, commonly called visible light, is tiny compared to the whole spectrum.
Many of the objects captured by the JWST give off visible light, as well as infrared. So, why bother looking at the sky using an infrared telescope? Some objects are only visible to us in infrared because they aren’t very bright (like planets that don’t emit visible light by themselves) or because dust is blocking the visible light. For objects that are really far away, the light they emit gets stretched out, going from visible to infrared, a phenomenon called redshifting, Alice Shapley, an astronomy professor at UCLA explained to me. This happens because the universe is expanding. The Carina nebula is within our home galaxy, so it’s not far away enough to get redshifted. But many galaxies in the deep field image are far away enough that the light they emit does get redshifted, leaving scientists to translate it back into a form that our eyes can understand.
To make the images circulating now, Shapley explained, the JWST used its infrared cameras to collect several “brightness images” in grayscale. Six filters each captured different wavelengths of infrared light. Back on Earth, each filter was assigned a color. The filter capturing the longest wavelength was red; the filter capturing the shortest wavelength was blue, with the other colors in between. By combining these images, the final composite image features all of the colors visible in the photos circulating now.
But if the Carina nebula or the swath of galaxies don’t technically “look like that,” why go through the trouble creating the colorful images? On a practical level, it helps scientists analyze them. Going through reams of infrared data and cross-referencing it with a grayscale image is difficult. But by assigning different wavelengths a color, scientists can pick out “objects of interest” that they’d like to study more, explains Alexei Fillipenko, a professor of astronomy at UC Berkeley. “If it were just a matrix of numbers or just a zillion numbers flashed across our TV screen, giving the digital value of the infrared radiation of a particular wavelength at a particular location in the sky … that’s not something that our eye-brain combination is developed evolutionarily to quickly analyze,” he said.
Another reason is “to capture people’s imaginations,” says Shapley. The telescope cost around $10 billion, so NASA has an incentive to show the taxpayers all that money and the many, many delays were all worth it. A bunch of gray images and data definitely would not trend on Twitter, but the images they shared were inescapable.
Along with capturing imaginations and showing everyone that NASA’s new toy works, there’s an even simpler reason to do all this: It looks pretty. Just take a minute to look at the “cosmic cliffs” lapping like a wave over inky blues and blacks. Think about it as a little art collaboration between scientific instruments and imagination. If we’re going to spend billions of dollars on a giant space telescope, these are the screensavers I want to be getting out of it.