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The James Webb Space Telescope: As Cool As It Gets


Last updated on May 1, 2022

On April 28, NASA released the first images from the James Webb Space Telescope(JWST), launched in December of 2021. The telescope’s purpose is to study the phases of cosmic history. At their creation, the first stars emitted UV and visible light. This light has shifted to infrared light through the expansion of the universe and is what JWST is looking for. 

There are four instruments aboard that pick up infrared light: the Near-Infrared Camera (NIRCam) which detects the light from the earliest stars and galaxies; the Near-Infrared Spectrograph (NIRSPEC) which characterizes the physical properties of the objects that the NIRCam finds; the Fine Guidance Sensor (FGS) which finetunes the data and images that the first two instruments create; and lastly, there is the Mid-Infrared Instrument (MIRI), which is the only instrument to look within the mid-infrared range rather than the near-infrared range. In the images above, NIRCam, NIRSPEC, and FGS all show millions of stars. MIRI’s images, which are pointed in the same direction as the other three, show a nebula. This is because it’s looking for longer wavelengths, which allows it to pick up on more than the other instruments. 

But before the telescope could start searching for these rays and imaging them, it had to first arrive at a special point in space called L2, where it is shielded from the Sun’s heat and light by the Earth. 

This shielding is imperative for the instruments to work properly. While heading toward the L2 point, a massive sunshield unfolded and shielded JWST. Because it is looking for longer wavelengths, MIRI needs to be much colder than the other instruments. The other three can operate at about 30 to 40 Kelvin (about -400 degrees Fahrenheit), while MIRI needs to be at a temperature no higher than 7 Kelvin (about -450 degrees Fahrenheit). 


On April 21st, JWST reached 7 Kelvin and all that was left was for the mirrors to finish cooling down as well. The primary mirrors are the massive gold-coated mirrors that give JWST its distinctive look. They reflect the light towards a secondary mirror, which is much smaller, which reflects the light into the instruments. This process focuses gathered light, generating a sharper image. 

Now that the first images have been released, Cycle 1, scientific advancement using the telescope’s images will most likely begin soon. Soon enough, we’ll be able to look back billions of years and see the creation of our universe. And that’s pretty cool.

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