In the shape of a hexagonal array of photographs of a single star, JWST has taken another step toward obtaining scientifically valuable photos. The array symbolizes each image captured by JWST’s 18 mirrors, which aren’t entirely focussed or aligned yet such that their reflected light converges at a single point. Launching a single 6.5-meter-wide (21-foot-wide) mirror into space is beyond humanity’s existing capabilities — even if it could be done, it would be a stretch. As a result, JWST is made up of 18 mirrors arranged in the now-familiar hexagonal configuration, which opened up like a flower a fortnight after launch.
These mirrors will eventually be focussed together, allowing the telescope’s equipment to absorb all of the combined light. They must, however, be positioned with an inaccuracy of less than 50 nanometers, or roughly a tenth of a visible light wavelength. It will take a long time to get there, far longer than it took to deploy the sun-shield and unfold the mirrors in the first place. JWST’s operators collected the first image of a star from each of the individual mirrors before merging their focus. HD 84406 was chosen as the designated star.
It may not be brilliant enough to merit a more interesting moniker, but there’s nothing in the sky that comes near enough to it in terms of brightness to further distort the image. There was also enough time to take a quick selfie in front of the mirror. Initially, the star’s spots were strewn throughout the camera field, not randomly but clearly haphazardly, spanning nearly a half degree of sky, roughly similar to a full moon.
The next stage was to build a nice array, which was done by a procedure known as Segment Image Identification. Because none of the mirrors have been brought entirely into focus, none of these photos are sharp. As you can see, some people are far closer to the goal than others. In a statement, Matthew Lallo of the Space Telescope Science Institute said, “We direct the segment dots into this array so that they have the same relative placements as the physical mirrors.” “This intuitive and natural way of visualizing changes in the segment spots in the context of the entire primary mirror gives the wavefront team an intuitive and natural way of visualizing changes in the segment spots in the context of the entire primary mirror gives the wavefront team an intuitive and natural way of visualizing changes in the segment spots in the context. We can now witness the primary mirror gradually take on its precise, desired shape!”
The team is presently working on the Segment Alignment stage, which should result in 18 crisp dots in the same relative locations. The telescope’s operators will go to “Image Stacking,” where the light will be merged if they are satisfied that each mirror is correctly focused. After then, there are four more phases to complete in order for the combination to operate. It will take three months to complete the process. While JWST has been routinely delayed on the ground, its activities in space have consistently outperformed expectations.
