The James Webb Space Telescope opened its doors, and it snapped a star into 18. But don't worry, this is just the first step in debugging its main mirror.
Original Puzzle (Source: NASA)
James Webb's main mirror is made up of 18 independent hexagonal lenses spliced together, so for the telescope optical system, the most core task, and the biggest difficulty, is to concentrate the light cast on the 18 lenses to a point, so that these small lenses work together to exert a large mirror effect.
On Feb. 2, the James Webb telescope began capturing images, and the team targeted a star, HD 84406, on the east side of The Big Dipper in the constellation Ursa Major. Since the optical path of the 18-sided lens was relatively dispersed and the coverage range was relatively large before the calibration was completed, the team appropriately expanded the imaging range to cover an area of almost a full moon. The 10 detectors on the telescope's near-infrared camera (NIRCam) generated 1560 images, equivalent to 54G's raw data, stitched together like a mosaic into a huge picture.
Stellar HD 84406 (Source: IAU and Sky & Telescope magazine)
Puzzle of the James Webb Telescope's First Light (Source: NASA)
Unsurprisingly, the team saw a lot of stars. They were delighted to find 18 images of hd 84406, like compound eyes of insects—images from each of the 18 lenses. After comparison, the team also successfully identified that these star points corresponded to the lens, so that they could adjust them one by one and slowly converge the light points into one point.
Staff identify the correspondence between the star point and the lens (Source: NASA)
Demonstration animation of the star point calibrated (Source: NASA)
HD 84406 is a helio-like star about 260 light-years away from Earth, with an apparent visual magnitude of about 6.94 magnitude, a mass of 1.4 times that of the Sun, and a surface temperature of 4900 K, which is really very similar to our Sun. This star, which is neither very bright nor very bright, is really suitable for the current James Webb to observe. What's more, there are no brighter stars in James Webb's field of view, so it is also particularly suitable for staff to locate and identify it.
Eventually, the 18 points will converge into one point (Source: NASA)
Over the next three months, the other three instruments will also reach the expected low temperatures and begin collecting data, and James Webb's images will become clearer, more detailed, and more complex. Now it seems that although there are still many things to do, everything is going well.
Selfie of the james Webb telescope mirror (Source: NASA)
Resources:
[1] Photons Received: Webb Sees Its First Star – 18 Times
(https://blogs.nasa.gov/webb/2022/02/11/photons-received-webb-sees-its-first-star-18-times/)
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