Webb Telescope reaches major milestone: All its light is in one place

NASA shared an image today indicating that it had successfully completed the image alignment stage of the James Webb Space Telescope. As of today, all 18 segments of the primary mirror are aligned so that a single star shows up as a single object. The path to commission the telescope keeps getting shorter as there are still more focusing steps required.

The telescope had to be held in a compact configuration to fit inside the launch vehicle, so the focus immediately after launch was on unfolding it. Extending the primary mirror, lowering the secondary mirror, and stretching out the multi-layer sunscreen were all part of the process.

It went incredibly smoothly to the surprise of many people. The focus has shifted since then. Each of the 18 mirrors in the primary mirror can be controlled separately. When the mirror was first put in place, there were 18 individual smudges on the secondary mirror.

Changes to the mirrors created a hexagonal array of smudges that replicated the arrangement of the primary mirror segments. The segments were shifted so that each one was focused on the center of the secondary mirror. The result? The star being imaged for this process has a single dot at the center of the telescope's field of view.

NASA is not done yet. The images are superimposed on top of each other in the same place. The goal is to have the segments act as a single mirror, which requires more careful focusing. Engineers will look for slight shifts in the image locations of the light's spectrum. It is possible to figure out which way the mirrors must be shifted.