What are the true colors of images from the James Webb Space Telescope?


NASA’s James Webb Space Telescope (JWST) is known for capturing our universe with unprecedented precision and sensitivity. Its images aren’t only scientifically useful but also beautiful. From the blue and gold of the Southern Ring Nebula to the pink, orange and purple of Cassiopeia A, JWST images render the universe in brilliant color.

The images are so stunning, you might wonder, —do these cosmic objects really look that colorful? What would they look like if we could see them with our own eyes, instead of through a telescope?

“The quickest answer is, we don’t know,” said Alyssa Pagan, a science visuals developer at the Space Telescope Science Institute (STScI) and part of the team that works to bring color to the JWST images. But one thing is for sure: You wouldn’t see the universe like this.

JWST is an infrared telescope, meaning it “looks” at the universe in wavelengths of light that are longer than that of red light, which has the longest wavelength we can detect with our eyes.

Related: How the James Webb Space Telescope’s infrared detectors will open new vistas in astronomy

If you could look directly at these objects, you might see something closer to images from telescopes that rely on visual light, like the Hubble Space Telescope, Pagan said. But even that comparison isn’t quite right, since Hubble is much bigger and more sensitive than the human eye. Also, visual-light telescopes might capture different features of an image than an infrared telescope would, even when focused on the same target.

So how are the colors for these spectacular images chosen, then? JWST targets are viewed through several filters attached to the telescope, which “see” in a certain range of wavelengths of infrared light. JWST’s Near Infrared Camera, the telescope’s main camera, has six filters, all of which capture slightly different images. Combining these images into a composite allows Pagan and Joe DePasquale, another science visual developer at the STScI for JWST, to create the full-color images.

When Pagan and DePasquale first receive the images, they appear in black and white. The colors are added to the image later, as the data from the various filters are translated into the spectrum of visible light, Pagan explained. The longest wavelengths appear red, while the shorter wavelengths are blue or purple.

“We are using that relationship with wavelengths and the color of light, and we’re just applying that to the infrared,” Pagan said.

Once each color has been added to the image, it might go through some additional alterations. Sometimes, the original colors can make an image look faded or dusty, and the colors are made more vivid to give it a sharper quality. The colors might also be shifted to emphasize certain hard-to-spot features.

Pagan and DePasquale also work with researchers to make sure the images are scientifically accurate, particularly if they are presented alongside a particular scientific finding, Pagan said. Though the color images don’t provide specific scientific data, they can help illustrate certain findings.

Sometimes they also can help scientists see areas they might want to research, Pagan said. For instance, the most distant objects in JWST’s first deep-field view — which appear red because light traveling such a distance had been stretched out — presented targets for research on the early universe when these objects would have existed as they appeared in the deep-field image.

The colors in JWST’s images may not be “real,” but don’t get the wrong idea — the colors aren’t meant to trick you, and they aren’t chosen only to look good. The images are intended to communicate as clearly as possible what JWST can see — and what our eyes can’t.

“We’re just trying to enhance things to make it more scientifically digestible and also engaging,” Pagan said.

The iconic Pillars of Creation. The Hubble Space Telescope's view on the left, the new James Webb Space Telescope photo on the right.

The iconic Pillars of Creation. The Hubble Space Telescope’s view on the left, the new James Webb Space Telescope photo on the right.

You can see some of the differences between images from visual-light and infrared telescopes by comparing images of the iconic Pillars of Creation taken by JWST and Hubble. While large portions of the pillars appear dark red in the Hubble image, the JWST image depicts most of the formation in golden and orange tones. This means that the visual light emitted by the pillars is longer wavelength (red) but a bit closer to the middle of the spectrum of infrared light depicted in the image.

Much of the hazy material that surrounds the pillars in the Hubble image, and even some of the materials of the pillars themselves, is also absent from the JWST image, meaning this portion of gas and dust is transparent in infrared. The JWST image also highlights more areas of star formation in red, which are obscured by thick clouds of gas and dust in the Hubble image.



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