Detail: The precision of the Fine Guidance Sensor on the Webb Telescope is quite impressive. Its ability to detect changes in a celestial object is said to be equivalent to a person in New York City being able to see the eye movement of someone blinking at the Canadian border more than 300 miles away.
The James Webb Space Telescope earlier this month started aligning its 18 mirrors, a mandatory, months-long process that involves the observatory's Near Infrared Camera (NIRCam) instrument. Eventually, we got to see what Webb saw when it gazed at its first star.
The sample image confirmed that NIRCam was working correctly, and that Webb was capturing light from the same star across each of its 18 primary mirror segments. And that's exactly what we saw, a single image with 18 seemingly random organized dots of starlight.
The next phase in the commissioning process involves using the telescopes 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 scope's fine steering mirror roughly three times a second to maintain a steady lock on its target.
Moving 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.