As light travels through space, it is stretched out by the expansion of the universe. This is why many of the most distant objects glow in the infrared, which has a longer wavelength than visible light. We can’t see this ancient light with the naked eye, but the James Webb Space Telescope (JWST) is designed to capture it, revealing some of the earliest galaxies ever formed.
        Aperture Masking: A perforated metal plate blocks out some of the light entering the telescope, allowing it to mimic an interferometer that combines data from multiple telescopes to achieve higher resolution than a single lens. This method brings out more detail in very bright objects in close proximity, such as two nearby stars in the sky.
       Micro Gate Array: A grid of 248,000 small gates can be opened or closed to measure the spectrum – the propagation of light down to its constituent wavelengths – at 100 points in one frame.
       Spectrometer: A grating or prism separates incident light into a spectrum to display the intensity of individual wavelengths.
       Cameras: JWST has three cameras – two that capture light in the near infrared wavelengths and one that captures light in the mid infrared wavelengths.
       Integral field unit: The combined camera and spectrometer captures an image along with the spectrum of each pixel, showing how light changes in the field of view.
        Coronagraphs: Glare from bright stars can block out faint light from planets and debris disks orbiting those stars. Coronographs are opaque circles that block bright starlight and allow weaker signals to pass through.
        Fine Guidance Sensor (FGS)/Near Infrared Imager and Slitless Spectrometer (NIRISS): The FGS is a pointing camera that helps point the telescope in the right direction. It is packaged with NIRISS which has a camera and a spectrometer that can capture near infrared images and spectra.
        Near Infrared Spectrometer (NIRSpec): This specialized spectrometer can simultaneously acquire 100 spectra through an array of microshutters. This is the first space instrument capable of performing spectral analysis of so many objects simultaneously.
        Near Infrared Camera (NIRCam): The only near infrared instrument with a coronagraph, NIRCam will be a key tool for studying exoplanets whose light would otherwise be obscured by the glare of nearby stars. It will capture high-resolution near-infrared images and spectra.
       Mid-Infrared Instrument (MIRI): This camera/spectrograph combination is the only instrument in the JWST that can see mid-infrared light emitted by cooler objects such as debris disks around stars and very distant galaxies.
        Scientists had to make adjustments to turn JWST’s raw data into something the human eye can appreciate, but its images are “real,” said Alyssa Pagan, a science vision engineer at the Space Telescope Science Institute. “Is this really what we would see if we were there? The answer is no, because our eyes are not designed to see in the infrared, and telescopes are much more sensitive to light than our eyes.” The telescope’s expanded field of view allows us to see these cosmic objects more realistically than our relatively limited eyes can. JWST can take pictures using up to 27 filters that capture different ranges of the infrared spectrum. Scientists first isolate the most useful dynamic range for a given image and scale the brightness values ​​to reveal as much detail as possible. They then assigned each infrared filter a color in the visible spectrum – the shortest wavelengths became blue, while the longer wavelengths became green and red. Put them together and you’re left with the normal white balance, contrast and color settings that any photographer is likely to make.
        While full color images are mesmerizing, many exciting discoveries are being made one wavelength at a time. Here, the NIRSpec instrument shows various features of the Tarantula Nebula through various filters. For example, atomic hydrogen (blue) radiates wavelengths from the central star and its surrounding bubbles. Between them are traces of molecular hydrogen (green) and complex hydrocarbons (red). Evidence suggests that the star cluster in the lower right corner of the frame is blowing dust and gas towards the central star.
       This article was originally published in Scientific American 327, 6, 42-45 (December 2022) as “Behind the Pictures”.
        Jen Christiansen is a senior graphics editor at Scientific American. Follow Christiansen on Twitter @ChristiansenJen
        is Senior Editor for Space and Physics at Scientific American. She holds a bachelor’s degree in astronomy and physics from Wesleyan University and a master’s degree in science journalism from the University of California, Santa Cruz. Follow Moskowitz on Twitter @ClaraMoskowitz. Photo courtesy of Nick Higgins.
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