The Colors in the James Webb Space Telescope Photos Are Fake
And that’s OK.Slate by Sarah Braner July 15, 2022
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.
More:
https://slate.com/technology/2022/07/james-webb-space-telescope-photos-colors-infrared.html