Detail: The accuracy of the Webb telescope’s fine guidance sensor is quite impressive. Its ability to detect changes in a celestial object is said to be equivalent to a person in New York being able to see the eye movement of someone blinking across the Canadian border from over 300 miles away.
Earlier this month, the James Webb Space Telescope began aligning its 18 mirrors, a mandatory months-long process that involves the observatory’s near-infrared camera (NIRCam) instrument. Finally, we got to see what Webb saw when he looked at his first star.
the sample picture confirmed that NIRCam was working correctly and that Webb was capturing light from the same star on each of its 18 primary mirror segments. And that’s exactly what we saw, a single image with 18 seemingly randomly arranged points of starlight.
The next phase of the commissioning process is to use the telescope’s Fine Guidance Sensor (FGS) to lock onto a guide star. The FGS measures the position of a guide star in its field of view 16 times per second and sends updates to the telescope’s thin steering mirror approximately three times per second to maintain a stable lock on its target.
Going forward, NASA said most of the mirror alignment process will be aided by the FGS, with NIRCam images being used to provide diagnostic information for further adjustments.